Read files in JavaScript | Articles

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0-10.359-2.786l-1.135-.063h-.063l-.458-.026c-.583-.036-1.172-.068-1.755-.094l.036.078c.234.615.396 1.255.479 1.906.042.453-.036 1.078-.224 1.88l-.203.828a24.99 24.99 0 0 1-.385 1.333l-.026.068v.036c-.068.203-.266.297-.438.229a.42.42 0 0 1-.203-.51v-.026l.042-.078.078-.292c.182-.589.344-1.177.479-1.776.161-.708.229-1.281.203-1.599-.016-.12-.031-.24-.052-.359a7.996 7.996 0 0 0-.521-1.708l-.052-.12-.031-.068-.026-.063c-.12-.271.057-.578.323-.563h.188l.531.042 2.12.104 1.135.083a28.14 28.14 0 0 1 10.573 2.823l.891.401c.172.078.266.307.188.505z"/> </svg></a> </div> </div> </div> <div class="wd-author"> <img class="devsite-landing-row-item-icon" alt="Pete LePage" src="https://web.dev/images/authors/petelepage.jpg" decoding="async" height="64" loading="lazy" width="64"> <div> <span> Pete LePage </span> <div class="wd-author__links"> <a href="https://twitter.com/petele" aria-label="Pete LePage on X" rel="me"> <svg xmlns="http://www.w3.org/2000/svg" width="22" height="22" viewBox="0 0 300 271"> <title>X</title> <path fill="currentColor" d="m236 0h46l-101 115 118 156h-92.6l-72.5-94.8-83 94.8h-46l107-123-113-148h94.9l65.5 86.6zm-16.1 244h25.5l-165-218h-27.4z"></path> </svg></a> <a href="https://github.com/petele" aria-label="Pete LePage on GitHub" rel="me"> <svg xmlns="http://www.w3.org/2000/svg" width="22" height="22" viewBox="0 0 32.6 31.8"> <title>GitHub</title> <path d="M16.3 0C7.3 0 0 7.3 0 16.3c0 7.2 4.7 13.3 11.1 15.5.8.1 1.1-.4 1.1-.8v-2.8c-4.5 1-5.5-2.2-5.5-2.2-.7-1.9-1.8-2.4-1.8-2.4-1.5-1 .1-1 .1-1 1.6.1 2.5 1.7 2.5 1.7 1.5 2.5 3.8 1.8 4.7 1.4.1-1.1.6-1.8 1-2.2-3.6-.4-7.4-1.8-7.4-8.1 0-1.8.6-3.2 1.7-4.4-.1-.3-.7-2 .2-4.2 0 0 1.4-.4 4.5 1.7 1.3-.4 2.7-.5 4.1-.5 1.4 0 2.8.2 4.1.5 3.1-2.1 4.5-1.7 4.5-1.7.9 2.2.3 3.9.2 4.3 1 1.1 1.7 2.6 1.7 4.4 0 6.3-3.8 7.6-7.4 8 .6.5 1.1 1.5 1.1 3V31c0 .4.3.9 1.1.8 6.5-2.2 11.1-8.3 11.1-15.5C32.6 7.3 25.3 0 16.3 0z" fill-rule="evenodd" clip-rule="evenodd" fill="currentColor" /> </svg></a> <a href="https://glitch.com/@petele" aria-label="Pete LePage on Glitch" rel="me"> <svg xmlns="http://www.w3.org/2000/svg" width="22" height="22" viewBox="0 0 32 32"> <title>Glitch</title> <path fill="currentColor" d="M31.734 16.76c-.385-.198-4.536 1.865-5.427 1.693-2.24-.401-1.828-.667-4.839-1.359-1.203-.266-1.031-.109-1.297-.307-.172-.135-.344-.161-.599-.401 4-.719 6.026-1.693 6.734-1.839.76-.146 5.161 1.958 5.427 1.469.266-.495-.964-1.578-.401-3.031.589-1.464-.693-2.422.016-3.583.719-1.161.573-2.932.396-3.026-.396-.203-4.531 1.865-5.438 1.693-2.24-.417-1.828-.682-4.839-1.359-1.203-.271-1.031-.12-1.297-.323-.266-.198-.521-.13-1.036-.974-.521-.839-6.51-2.13-6.906-2.13-.828 0-2.375 2.13-2.375 2.13s-.599 0-2.401.094c-1.802.094-3.375.896-5.495 2.563C-.173 9.737.134 11.414.134 11.414s1.969.667 1.969 1.042c0 .359-1.729.802-1.729.802 1.12 1.411 4.583 2.745 5.464 2.745h.693c-1.438.281-2.823 1.068-4.583 2.438-2.12 1.698-1.813 3.375-1.813 3.375s1.969.667 1.969 1.026-1.729.802-1.729.802c1.12 1.427 4.583 2.76 5.464 2.76.844 0 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href="https://techhub.social/@petele" aria-label="Pete LePage on Mastodon" rel="me"> <svg xmlns="http://www.w3.org/2000/svg" width="22" height="22" viewBox="0 0 16 16"> <title>Mastodon</title> <path fill="currentColor" d="M 15.659 9.592 C 15.424 10.72 13.553 11.956 11.404 12.195 C 10.283 12.32 9.18 12.434 8.003 12.384 C 6.079 12.302 4.56 11.956 4.56 11.956 C 4.56 12.13 4.572 12.297 4.595 12.452 C 4.845 14.224 6.478 14.33 8.025 14.379 C 9.586 14.429 10.976 14.02 10.976 14.02 L 11.04 15.337 C 11.04 15.337 9.948 15.884 8.003 15.984 C 6.93 16.039 5.598 15.959 4.047 15.576 C 0.683 14.746 0.104 11.4 0.015 8.006 C -0.012 6.998 0.005 6.048 0.005 5.253 C 0.005 1.782 2.443 0.765 2.443 0.765 C 3.672 0.238 5.782 0.017 7.975 0 L 8.029 0 C 10.221 0.017 12.332 0.238 13.561 0.765 C 13.561 0.765 15.999 1.782 15.999 5.253 C 15.999 5.253 16.03 7.814 15.659 9.592 Z M 13.124 5.522 L 13.124 9.725 L 11.339 9.725 L 11.339 5.646 C 11.339 4.786 10.951 4.35 10.175 4.35 C 9.317 4.35 8.887 4.867 8.887 5.891 L 8.887 8.124 L 7.113 8.124 L 7.113 5.891 C 7.113 4.867 6.683 4.35 5.825 4.35 C 5.049 4.35 4.661 4.786 4.661 5.646 L 4.661 9.725 L 2.876 9.725 L 2.876 5.522 C 2.876 4.663 3.111 3.981 3.582 3.476 C 4.067 2.971 4.703 2.712 5.493 2.712 C 6.406 2.712 7.098 3.039 7.555 3.695 L 8 4.39 L 8.445 3.695 C 8.902 3.039 9.594 2.712 10.507 2.712 C 11.297 2.712 11.933 2.971 12.418 3.476 C 12.889 3.981 13.124 4.663 13.124 5.522 Z" style="stroke:none;stroke-miterlimit:10;fill-rule:evenodd;"></path> </svg></a> <a href="https://petelepage.com/" aria-label="Pete LePage's homepage" rel="me"> <svg xmlns="http://www.w3.org/2000/svg" width="22" height="22" viewBox="0 0 30 30"> <title>Homepage</title> <circle cx="14.5" cy="14.5" r="13.5" stroke-width="2" stroke-miterlimit="10" fill="none" stroke="currentColor" /> <ellipse cx="14.5" cy="14.5" rx="6.1" ry="13.5" stroke-width="2" stroke-miterlimit="10" fill="none" stroke="currentColor" /> <path d="M1.6 9.6h25.8M1.6 19.4h25.8" stroke-width="2" stroke-miterlimit="10" fill="none" stroke="currentColor" /> </svg></a> </div> </div> </div> <div class="wd-author"> <img class="devsite-landing-row-item-icon" alt="Thomas Steiner" src="https://web.dev/images/authors/thomassteiner.jpg" decoding="async" height="64" loading="lazy" width="64"> <div> <span> Thomas Steiner </span> <div class="wd-author__links"> <a href="https://github.com/tomayac" aria-label="Thomas Steiner on GitHub" rel="me"> <svg xmlns="http://www.w3.org/2000/svg" width="22" height="22" viewBox="0 0 32.6 31.8"> <title>GitHub</title> <path d="M16.3 0C7.3 0 0 7.3 0 16.3c0 7.2 4.7 13.3 11.1 15.5.8.1 1.1-.4 1.1-.8v-2.8c-4.5 1-5.5-2.2-5.5-2.2-.7-1.9-1.8-2.4-1.8-2.4-1.5-1 .1-1 .1-1 1.6.1 2.5 1.7 2.5 1.7 1.5 2.5 3.8 1.8 4.7 1.4.1-1.1.6-1.8 1-2.2-3.6-.4-7.4-1.8-7.4-8.1 0-1.8.6-3.2 1.7-4.4-.1-.3-.7-2 .2-4.2 0 0 1.4-.4 4.5 1.7 1.3-.4 2.7-.5 4.1-.5 1.4 0 2.8.2 4.1.5 3.1-2.1 4.5-1.7 4.5-1.7.9 2.2.3 3.9.2 4.3 1 1.1 1.7 2.6 1.7 4.4 0 6.3-3.8 7.6-7.4 8 .6.5 1.1 1.5 1.1 3V31c0 .4.3.9 1.1.8 6.5-2.2 11.1-8.3 11.1-15.5C32.6 7.3 25.3 0 16.3 0z" fill-rule="evenodd" clip-rule="evenodd" fill="currentColor" /> </svg></a> <a href="https://glitch.com/@tomayac" aria-label="Thomas Steiner on Glitch" rel="me"> <svg xmlns="http://www.w3.org/2000/svg" width="22" height="22" viewBox="0 0 32 32"> <title>Glitch</title> <path fill="currentColor" d="M31.734 16.76c-.385-.198-4.536 1.865-5.427 1.693-2.24-.401-1.828-.667-4.839-1.359-1.203-.266-1.031-.109-1.297-.307-.172-.135-.344-.161-.599-.401 4-.719 6.026-1.693 6.734-1.839.76-.146 5.161 1.958 5.427 1.469.266-.495-.964-1.578-.401-3.031.589-1.464-.693-2.422.016-3.583.719-1.161.573-2.932.396-3.026-.396-.203-4.531 1.865-5.438 1.693-2.24-.417-1.828-.682-4.839-1.359-1.203-.271-1.031-.12-1.297-.323-.266-.198-.521-.13-1.036-.974-.521-.839-6.51-2.13-6.906-2.13-.828 0-2.375 2.13-2.375 2.13s-.599 0-2.401.094c-1.802.094-3.375.896-5.495 2.563C-.173 9.737.134 11.414.134 11.414s1.969.667 1.969 1.042c0 .359-1.729.802-1.729.802 1.12 1.411 4.583 2.745 5.464 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1.135.083a28.14 28.14 0 0 1 10.573 2.823l.891.401c.172.078.266.307.188.505z"/> </svg></a> <a href="https://www.linkedin.com/in/thomassteinerlinkedin" aria-label="Thomas Steiner on LinkedIn" rel="me"> <svg xmlns="http://www.w3.org/2000/svg" width="22" height="22" viewBox="0 0 200 200"> <title>LinkedIn</title> <path d="M185.2 0H14.8C6.6 0 0 6.4 0 14.3v171.3c0 7.9 6.6 14.3 14.8 14.3h170.4c8.1 0 14.8-6.4 14.8-14.3V14.3C199.9 6.4 193.3 0 185.2 0zM60.6 167.3H30.4V77.1h30.2v90.2zM45.5 64.8h-.2c-10.1 0-16.7-6.9-16.7-15.6 0-8.8 6.7-15.6 17.1-15.6 10.3 0 16.7 6.7 16.9 15.6 0 8.6-6.5 15.6-17.1 15.6zm124 102.5h-30.2V119c0-12.1-4.4-20.4-15.3-20.4-8.4 0-13.3 5.6-15.5 11-.8 1.9-1 4.6-1 7.3v50.4H77.3s.4-81.8 0-90.3h30.2v12.8c4-6.1 11.2-14.9 27.2-14.9 19.9 0 34.8 12.9 34.8 40.6v51.8zm-62.2-77.1c0-.1.1-.2.2-.3v.3h-.2z" fill="currentColor" /> </svg></a> <a href="https://toot.cafe/@tomayac" aria-label="Thomas Steiner on Mastodon" rel="me"> <svg xmlns="http://www.w3.org/2000/svg" width="22" height="22" 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70.281-63.111-64.76-33.89-129.52 80.986-149.071-65.72 11.185-139.6-7.295-159.875-79.748C9.945 203.659 0 75.291 0 57.946 0-28.906 76.135-1.612 123.121 33.664Z"/> </svg> </a> <a href="https://blog.tomayac.com/" aria-label="Thomas Steiner's homepage" rel="me"> <svg xmlns="http://www.w3.org/2000/svg" width="22" height="22" viewBox="0 0 30 30"> <title>Homepage</title> <circle cx="14.5" cy="14.5" r="13.5" stroke-width="2" stroke-miterlimit="10" fill="none" stroke="currentColor" /> <ellipse cx="14.5" cy="14.5" rx="6.1" ry="13.5" stroke-width="2" stroke-miterlimit="10" fill="none" stroke="currentColor" /> <path d="M1.6 9.6h25.8M1.6 19.4h25.8" stroke-width="2" stroke-miterlimit="10" fill="none" stroke="currentColor" /> </svg></a> </div> </div> </div> </div></p> <p>Selecting and interacting with files on the user's local device is one of the most commonly used features of the web. It allows users to select files and upload them to a server, for example, when sharing photos or submitting tax documents. It also allows sites to read and manipulate them without ever having to transfer the data across the network. This page walks through how to use JavaScript to interact with files.</p> <h2 id="file-system-access-api" data-text="The modern File System Access API" tabindex="-1">The modern File System Access API</h2> <p>The File System Access API provides a way to read from and write to files and directories on the user's local system. It's available in most Chromium-based browsers such as Chrome and Edge. To learn more about it, refer to <a href="https://developer.chrome.com/docs/capabilities/web-apis/file-system-access">The File System Access API</a>.</p> <p>Because the File System Access API isn't compatible with all browsers, we recommend using <a href="https://github.com/GoogleChromeLabs/browser-fs-access">browser-fs-access</a>, a helper library that uses the new API wherever it's available and falls back to legacy approaches when it isn't.</p> <h2 id="legacy-methods" data-text="Work with files, the classic way" tabindex="-1">Work with files, the classic way</h2> <p>This guide shows you how to interact with files using legacy JavaScript methods.</p> <h2 id="select" data-text="Select files" tabindex="-1">Select files</h2> <p>There are two primary ways of selecting files: using <a href="#select-input">the HTML input element</a>, and using a <a href="#select-dnd">drag-and-drop zone</a>.</p> <h3 id="select-input" data-text="HTML input element" tabindex="-1">HTML input element</h3> <p>The easiest way for users to select files is using the <a href="https://developer.mozilla.org/docs/Web/HTML/Element/input/file"><code translate="no" dir="ltr"><input type="file"></code></a> element, which is supported in every major browser. When clicked, it lets a user select a file, or multiple files if the <a href="https://developer.mozilla.org/docs/Web/HTML/Element/input/file#Additional_attributes"><code translate="no" dir="ltr">multiple</code></a> attribute is included, using their operating system's built-in file selection UI. When the user finishes selecting a file or files, the element's <code translate="no" dir="ltr">change</code> event fires. You can access the list of files from <code translate="no" dir="ltr">event.target.files</code>, which is a <a href="https://developer.mozilla.org/docs/Web/API/FileList"><code translate="no" dir="ltr">FileList</code></a> object. Each item in the <code translate="no" dir="ltr">FileList</code> is a <a href="https://developer.mozilla.org/docs/Web/API/File"><code translate="no" dir="ltr">File</code></a> object.</p> <div></div><devsite-code><pre class="devsite-click-to-copy" translate="no" dir="ltr" is-upgraded syntax="HTML"><code translate="no" dir="ltr"> <input type="file" id="file-selector" multiple> <script> const fileSelector = document.getElementById('file-selector'); fileSelector.addEventListener('change', (event) => { const fileList = event.target.files; console.log(fileList); }); </script> </code></pre></devsite-code><aside class="note"><strong>Note:</strong><span> Check whether the <a href="https://developer.chrome.com/articles/file-system-access/#ask-the-user-to-pick-a-file-to-read"><code translate="no" dir="ltr">window.showOpenFilePicker()</code></a> method is a viable alternative for your use case. It provides a file handle so you can write back to a file, in addition to reading. This method can be <a href="https://github.com/GoogleChromeLabs/browser-fs-access#opening-files">polyfilled</a>.</span></aside> <p>The following example lets a user select multiple files using their operating system's built-in file selection UI and then logs each selected file to the console.</p> <div class="wd-embed" style="height: 480px;"> <iframe allow="camera; clipboard-read; clipboard-write; encrypted-media; geolocation; microphone; midi" loading="lazy" src="https://glitch.com/embed/#!/embed/input-type-file?attributionHidden=true&sidebarCollapsed=true&previewSize=100" style="height: 100%; width: 100%; border: 0;" title="input-type-file on Glitch" ></iframe> </div> <h4 id="accept" data-text="Limit the types of files users can select" tabindex="-1">Limit the types of files users can select</h4> <p>In some cases, you might want to limit the types of files users can select. For example, an image editing app should only accept images, not text files. To set file type restrictions, add an <a href="https://developer.mozilla.org/docs/Web/HTML/Element/input/file#Additional_attributes"><code translate="no" dir="ltr">accept</code></a> attribute to the input element to specify which file types are accepted:</p> <div></div><devsite-code><pre class="devsite-click-to-copy" translate="no" dir="ltr" is-upgraded syntax="HTML"><code translate="no" dir="ltr"><input type="file" id="file-selector" accept=".jpg, .jpeg, .png"> </code></pre></devsite-code> <h3 id="select-dnd" data-text="Custom drag-and-drop" tabindex="-1">Custom drag-and-drop</h3> <p>In some browsers, the <code translate="no" dir="ltr"><input type="file"></code> element is also a drop target, allowing users to drag-and-drop files into your app. However, this drop target is small and can be hard to use. Instead, after you provide core features using an <code translate="no" dir="ltr"><input type="file"></code> element, you can provide a large, custom drag-and-drop surface.</p> <aside class="note"><strong>Note:</strong><span> Check whether the <a href="https://developer.chrome.com/articles/file-system-access/#drag-and-drop-integration"><code translate="no" dir="ltr">DataTransferItem.getAsFileSystemHandle()</code></a> method is a viable alternative for your use case. It provides a file handle so you can write back to a file, in addition to reading.</span></aside> <h4 id="choose-drop-zone" data-text="Choose your drop zone" tabindex="-1">Choose your drop zone</h4> <p>Your drop surface depends on the design of your application. You might only want part of the window to be a drop surface, but you can use the entire window.</p> <figure> <img src="/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4.png" alt="A screenshot of Squoosh, an image compression web app." width="800" height="589" srcset="https://web.dev/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4_36.png 36w,https://web.dev/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4_48.png 48w,https://web.dev/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4_72.png 72w,https://web.dev/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4_96.png 96w,https://web.dev/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4_480.png 480w,https://web.dev/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4_720.png 720w,https://web.dev/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4_856.png 856w,https://web.dev/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4_960.png 960w,https://web.dev/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4_1440.png 1440w,https://web.dev/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4_1920.png 1920w,https://web.dev/static/articles/read-files/image/a-screenshot-squoosh-i-9973c866302e4_2880.png 2880w" sizes="(max-width: 840px) 100vw, 856px"> <figcaption class="wd-caption"> Squoosh makes the entire window a drop zone. </figcaption> </figure> <p>The image compression app Squoosh lets user drag an image anywhere into the window, and click <strong>select an image</strong> to invoke the <code translate="no" dir="ltr"><input type="file"></code> element. Whatever you choose as your drop zone, make sure it's clear to the user that they can drag files onto that surface.</p> <h4 id="define-drop-zone" data-text="Define the drop zone" tabindex="-1">Define the drop zone</h4> <p>To enable an element as a drag-and-drop zone, create listeners for two events: <a href="https://developer.mozilla.org/docs/Web/API/Document/dragover_event"><code translate="no" dir="ltr">dragover</code></a> and <a href="https://developer.mozilla.org/docs/Web/API/Document/drop_event"><code translate="no" dir="ltr">drop</code></a>. The <code translate="no" dir="ltr">dragover</code> event updates the browser UI to visually indicate that the drag-and-drop action is creating a copy of the file. The <code translate="no" dir="ltr">drop</code> event fires after the user drops the files onto the surface. As with the input element, you can access the list of files from <code translate="no" dir="ltr">event.dataTransfer.files</code>, which is a <a href="https://developer.mozilla.org/docs/Web/API/FileList"><code translate="no" dir="ltr">FileList</code></a> object. Each item in the <code translate="no" dir="ltr">FileList</code> is a <a href="https://developer.mozilla.org/docs/Web/API/File"><code translate="no" dir="ltr">File</code></a> object.</p> <div></div><devsite-code><pre class="devsite-click-to-copy" translate="no" dir="ltr" is-upgraded syntax="JavaScript"><code translate="no" dir="ltr"><span class="devsite-syntax-kd">const</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">dropArea</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nb">document</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">getElementById</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-s1">'drop-area'</span><span class="devsite-syntax-p">);</span> <span class="devsite-syntax-nx">dropArea</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">addEventListener</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-s1">'dragover'</span><span class="devsite-syntax-p">,</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-nx">event</span><span class="devsite-syntax-p">)</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span>><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">{</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">event</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">stopPropagation</span><span class="devsite-syntax-p">();</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">event</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">preventDefault</span><span class="devsite-syntax-p">();</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-c1">// Style the drag-and-drop as a "copy file" operation.</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">event</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">dataTransfer</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">dropEffect</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-s1">'copy'</span><span class="devsite-syntax-p">;</span> <span class="devsite-syntax-p">});</span> <span class="devsite-syntax-nx">dropArea</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">addEventListener</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-s1">'drop'</span><span class="devsite-syntax-p">,</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-nx">event</span><span class="devsite-syntax-p">)</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span>><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">{</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">event</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">stopPropagation</span><span class="devsite-syntax-p">();</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">event</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">preventDefault</span><span class="devsite-syntax-p">();</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-kd">const</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">fileList</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">event</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">dataTransfer</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">files</span><span class="devsite-syntax-p">;</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">console</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">log</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-nx">fileList</span><span class="devsite-syntax-p">);</span> <span class="devsite-syntax-p">});</span> </code></pre></devsite-code> <p><a href="https://developer.mozilla.org/docs/Web/API/Event/stopPropagation"><code translate="no" dir="ltr">event.stopPropagation()</code></a> and <a href="https://developer.mozilla.org/docs/Web/API/Event/preventDefault"><code translate="no" dir="ltr">event.preventDefault()</code></a> stop the browser's default behavior and let your code run instead. Without them, the browser would otherwise navigate away from your page and open the files the user dropped into the browser window.</p> <p>For a live demonstration, refer to <a href="https://custom-drag-and-drop.glitch.me/">Custom drag-and-drop</a>.</p> <h3 id="directories" data-text="What about directories?" tabindex="-1">What about directories?</h3> <p>Unfortunately, there isn't a good way to access a directory using JavaScript.</p> <p>The <a href="https://developer.mozilla.org/docs/Web/API/HTMLInputElement/webkitdirectory"><code translate="no" dir="ltr">webkitdirectory</code></a> attribute on the <code translate="no" dir="ltr"><input type="file"></code> element lets the user choose a directory or directories. It's <a href="https://caniuse.com/#search=webkitdirectory">supported in most major browsers</a> except for Firefox for Android and Safari on iOS.</p> <aside class="note"><strong>Note:</strong><span> Check whether the <a href="https://developer.chrome.com/articles/file-system-access/#opening-a-directory-and-enumerating-its-contents"><code translate="no" dir="ltr">window.showDirectoryPicker()</code></a> method is a viable alternative for your use case. It provides a directory handle so you can write back to a directory, in addition to reading. This method can be <a href="https://github.com/GoogleChromeLabs/browser-fs-access#opening-directories">polyfilled</a>.</span></aside> <p>If drag-and-drop is enabled, a user might try to drag a directory into the drop zone. When the drop event fires, it includes a <code translate="no" dir="ltr">File</code> object for the directory, but doesn't provide access to any of the files in the directory.</p> <h2 id="read-metadata" data-text="Read file metadata" tabindex="-1">Read file metadata</h2> <p>The <a href="https://developer.mozilla.org/docs/Web/API/File"><code translate="no" dir="ltr">File</code></a> object contains metadata about the file. Most browsers provide the filename, the size of the file, and the MIME type, though depending on the platform, different browsers might provide different or additional information.</p> <div></div><devsite-code><pre class="devsite-click-to-copy" translate="no" dir="ltr" is-upgraded syntax="JavaScript"><code translate="no" dir="ltr"><span class="devsite-syntax-kd">function</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">getMetadataForFileList</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-nx">fileList</span><span class="devsite-syntax-p">)</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">{</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-k">for</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-kd">const</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-k">of</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">fileList</span><span class="devsite-syntax-p">)</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">{</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-c1">// Not supported in Safari for iOS.</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-kd">const</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">name</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">name</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">?</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">name</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">:</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-s1">'NOT SUPPORTED'</span><span class="devsite-syntax-p">;</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-c1">// Not supported in Firefox for Android or Opera for Android.</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-kd">const</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">type</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">type</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">?</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">type</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">:</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-s1">'NOT SUPPORTED'</span><span class="devsite-syntax-p">;</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-c1">// Unknown cross-browser support.</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-kd">const</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">size</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">size</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">?</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">size</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">:</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-s1">'NOT SUPPORTED'</span><span class="devsite-syntax-p">;</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">console</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">log</span><span class="devsite-syntax-p">({</span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">,</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">name</span><span class="devsite-syntax-p">,</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">type</span><span class="devsite-syntax-p">,</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">size</span><span class="devsite-syntax-p">});</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">}</span> <span class="devsite-syntax-p">}</span> </code></pre></devsite-code> <p>You can see this in action in the <a href="https://input-type-file.glitch.me/"><code translate="no" dir="ltr">input-type-file</code></a> demo.</p> <h2 id="read-content" data-text="Read a file's content" tabindex="-1">Read a file's content</h2> <p>Use <a href="https://developer.mozilla.org/docs/Web/API/FileReader"><code translate="no" dir="ltr">FileReader</code></a> to read the content of a <code translate="no" dir="ltr">File</code> object into memory. You can tell <code translate="no" dir="ltr">FileReader</code> to read a file as an <a href="https://developer.mozilla.org/docs/Web/API/FileReader/readAsArrayBuffer">array buffer</a>, a <a href="https://developer.mozilla.org/docs/Web/API/FileReader/readAsDataURL">data URL</a>, or <a href="https://developer.mozilla.org/docs/Web/API/FileReader/readAsText">text</a>:</p> <div></div><devsite-code><pre class="devsite-click-to-copy" translate="no" dir="ltr" is-upgraded syntax="JavaScript"><code translate="no" dir="ltr"><span class="devsite-syntax-kd">function</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">readImage</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">)</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">{</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-c1">// Check if the file is an image.</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-k">if</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">type</span><span class="devsite-syntax-w"> && </span><span class="devsite-syntax-o">!</span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">type</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">startsWith</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-s1">'image/'</span><span class="devsite-syntax-p">))</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">{</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">console</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">log</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-s1">'File is not an image.'</span><span class="devsite-syntax-p">,</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">type</span><span class="devsite-syntax-p">,</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">);</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-k">return</span><span class="devsite-syntax-p">;</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">}</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-kd">const</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">reader</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-ow">new</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">FileReader</span><span class="devsite-syntax-p">();</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">reader</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">addEventListener</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-s1">'load'</span><span class="devsite-syntax-p">,</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-nx">event</span><span class="devsite-syntax-p">)</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span>><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">{</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">img</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">src</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">event</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">target</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">result</span><span class="devsite-syntax-p">;</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">});</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-nx">reader</span><span class="devsite-syntax-p">.</span><span class="devsite-syntax-nx">readAsDataURL</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-nx">file</span><span class="devsite-syntax-p">);</span> <span class="devsite-syntax-p">}</span> </code></pre></devsite-code> <p>This example reads a <code translate="no" dir="ltr">File</code> provided by the user, then converts it to a data URL, and uses that data URL to display the image in an <code translate="no" dir="ltr">img</code> element. To learn how to verify that the user has selected an image file, refer to the <a href="https://read-image-file.glitch.me/"><code translate="no" dir="ltr">read-image-file</code></a> demo.</p> <div class="wd-embed" style="height: 480px;"> <iframe allow="camera; clipboard-read; clipboard-write; encrypted-media; geolocation; microphone; midi" loading="lazy" src="https://glitch.com/embed/#!/embed/read-image-file?attributionHidden=true&sidebarCollapsed=true&previewSize=100" style="height: 100%; width: 100%; border: 0;" title="read-image-file on Glitch" ></iframe> </div> <h3 id="monitor-progress" data-text="Monitor the progress of a file read" tabindex="-1">Monitor the progress of a file read</h3> <p>When reading large files, it can be helpful to provide some UX to tell the user how far the read has progressed. For that, use the <a href="https://developer.mozilla.org/docs/Web/API/FileReader/progress_event"><code translate="no" dir="ltr">progress</code></a> event provided by <code translate="no" dir="ltr">FileReader</code>. The <code translate="no" dir="ltr">progress</code> event has two properties: <code translate="no" dir="ltr">loaded</code> (the amount read) and <code translate="no" dir="ltr">total</code> (the amount to read).</p> <div></div><devsite-code><pre class="devsite-click-to-copy" translate="no" dir="ltr" is-upgraded syntax="GDScript"><code translate="no" dir="ltr"><span class="devsite-syntax-n">function</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">readFile</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-n">file</span><span class="devsite-syntax-p">)</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">{</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-k">const</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">reader</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">new</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">FileReader</span><span class="devsite-syntax-p">();</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">reader</span><span class="devsite-syntax-o">.</span><span class="devsite-syntax-n">addEventListener</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-s1">'load'</span><span class="devsite-syntax-p">,</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-n">event</span><span class="devsite-syntax-p">)</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span>><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">{</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-k">const</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">result</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">event</span><span class="devsite-syntax-o">.</span><span class="devsite-syntax-n">target</span><span class="devsite-syntax-o">.</span><span class="devsite-syntax-n">result</span><span class="devsite-syntax-p">;</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">//</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">Do</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">something</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">with</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">result</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">});</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">reader</span><span class="devsite-syntax-o">.</span><span class="devsite-syntax-n">addEventListener</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-s1">'progress'</span><span class="devsite-syntax-p">,</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-n">event</span><span class="devsite-syntax-p">)</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span>><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">{</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-k">if</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-n">event</span><span class="devsite-syntax-o">.</span><span class="devsite-syntax-n">loaded</span><span class="devsite-syntax-w"> && </span><span class="devsite-syntax-n">event</span><span class="devsite-syntax-o">.</span><span class="devsite-syntax-n">total</span><span class="devsite-syntax-p">)</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">{</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-k">const</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">percent</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">=</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-n">event</span><span class="devsite-syntax-o">.</span><span class="devsite-syntax-n">loaded</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">/</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">event</span><span class="devsite-syntax-o">.</span><span class="devsite-syntax-n">total</span><span class="devsite-syntax-p">)</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">*</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-mi">100</span><span class="devsite-syntax-p">;</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">console</span><span class="devsite-syntax-o">.</span><span class="devsite-syntax-n">log</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-err">`</span><span class="devsite-syntax-n">Progress</span><span class="devsite-syntax-p">:</span><span class="devsite-syntax-w"> </span><span class="devsite-syntax-o">$</span><span class="devsite-syntax-p">{</span><span class="devsite-syntax-n">Math</span><span class="devsite-syntax-o">.</span><span class="devsite-syntax-n">round</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-n">percent</span><span class="devsite-syntax-p">)}</span><span class="devsite-syntax-err">`</span><span class="devsite-syntax-p">);</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">}</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-p">});</span> <span class="devsite-syntax-w"> </span><span class="devsite-syntax-n">reader</span><span class="devsite-syntax-o">.</span><span class="devsite-syntax-n">readAsDataURL</span><span class="devsite-syntax-p">(</span><span class="devsite-syntax-n">file</span><span class="devsite-syntax-p">);</span> <span class="devsite-syntax-p">}</span> </code></pre></devsite-code> <p>Hero image by Vincent Botta from <a href="https://unsplash.com/photos/bv_rJXpNU9I">Unsplash</a></p> </div> <devsite-thumb-rating position="footer"> </devsite-thumb-rating> <div class="devsite-floating-action-buttons"> </div> </article> <devsite-content-footer class="nocontent"> <p>Except as otherwise noted, the content of this page is licensed under the <a href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 License</a>, and code samples are licensed under the <a href="https://www.apache.org/licenses/LICENSE-2.0">Apache 2.0 License</a>. 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