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href="/resources/videos">Videos</a></li><li class="nav-item"><a class="nav-link" href="/tutorials">Tutorials</a></li></ul></li><li class="nav-item"><a class="nav-link collapsible" data-toggle="collapse" href="#sidenav-10" role="button" aria-expanded="true" aria-controls="sidenav-10">Related sites</a><ul class="nav flex-column flex-nowrap collapse show" id="sidenav-10"><li class="nav-item"><a class="nav-link" href="https://api.dart.dev" target="_blank" rel="noopener">API reference</a></li><li class="nav-item"><a class="nav-link" href="https://medium.com/dartlang" target="_blank" rel="noopener">Blog</a></li><li class="nav-item"><a class="nav-link" href="https://dartpad.dev" target="_blank" rel="noopener">DartPad (online editor)</a></li><li class="nav-item"><a class="nav-link" href="https://flutter.dev" target="_blank" rel="noopener">Flutter</a></li><li class="nav-item"><a class="nav-link" href="https://pub.dev" target="_blank" rel="noopener">Package site</a></li></ul></li></ul></div></div><main id="page-content"><div id="site-toc--side" class="site-toc"><header class="site-toc__title">Contents</header><ul class="section-nav"><li class="toc-entry nav-item"><a class="nav-link" href="#overview">Overview</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#using-dart-devtools">Getting started with Dart DevTools</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#getting-command-line-tool-packages">Getting command-line tool packages</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#debugging">Debugging production code</a><ul class="nav"><li class="toc-entry nav-item"><a class="nav-link" href="#dart2js-debugging-chrome">Chrome</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#dart2js-debugging-ie">Edge</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#dart2js-debugging-firefox">Firefox</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#dart2js-debugging-safari">Safari</a></li></ul></li><li class="toc-entry nav-item"><a class="nav-link" href="#resources">Resources</a></li></ul></div><article><div class="content"><div id="site-content-title"><h1>Debugging Dart web apps</h1></div><div id="site-toc--inline" class="site-toc"><header class="site-toc__title">Contents</header><ul class="section-nav"><li class="toc-entry"><a href="#overview">Overview</a></li><li class="toc-entry"><a href="#using-dart-devtools">Getting started with Dart DevTools</a></li><li class="toc-entry"><a href="#getting-command-line-tool-packages">Getting command-line tool packages</a></li><li class="toc-entry"><a href="#debugging">Debugging production code</a><ul><li class="toc-entry"><a href="#dart2js-debugging-chrome">Chrome</a></li><li class="toc-entry"><a href="#dart2js-debugging-ie">Edge</a></li><li class="toc-entry"><a href="#dart2js-debugging-firefox">Firefox</a></li><li class="toc-entry"><a href="#dart2js-debugging-safari">Safari</a></li></ul></li><li class="toc-entry"><a href="#resources">Resources</a></li></ul></div><p>You can use a <a href="/tools#editors">Dart IDE</a>, <a href="/tools/dart-devtools">Dart DevTools</a>, and browser tools such as <a href="https://developer.chrome.com/docs/devtools/">Chrome DevTools</a> to debug your Dart web apps.</p><ul><li>To debug your app's logic, use your IDE, Dart DevTools, or browser tools. Dart DevTools has better support than browser tools for inspecting and automatically reloading Dart code.</li><li>To debug your app's appearance (HTML/CSS) and performance, use your IDE or browser tools such as Chrome DevTools.</li></ul><div class="header-wrapper"><h2 id="overview">Overview</h2><a class="heading-link" href="#overview" aria-label="Link to 'Overview' section">#</a></div><p>To serve your app, use <code>webdev serve</code> (either at the command line or through your IDE) to start up the Dart development compiler. To enable Dart DevTools, add the <code>--debug</code> or <code>--debug-extension</code> option (at the command line or through your IDE):</p><div class="code-block-wrapper language-console"><div class="code-block-body"><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#222222">$ webdev serve --debug</span></span></code></pre></div></div><p>When running your app using the <code>--debug</code> flag of <code>webdev</code>, you can open Dart DevTools by pressing <kbd>Alt</kbd>+<kbd>D</kbd> (or <kbd>Option</kbd>+<kbd>D</kbd> on macOS).</p><p>To open Chrome DevTools, press <kbd>Control</kbd>+<kbd>Shift</kbd>+<kbd>I</kbd> (or <kbd>Command</kbd>+<kbd>Option</kbd>+<kbd>I</kbd> on macOS). If you want to debug your app using Chrome DevTools, you can use <a href="https://developer.chrome.com/docs/devtools/javascript/source-maps/">source maps</a> to display your Dart source files instead of the JavaScript that the compiler produces. For more information on using Chrome DevTools, see the <a href="https://developer.chrome.com/docs/devtools/">Chrome DevTools documentation.</a></p><p>To use the Dart DevTools or Chrome DevTools to debug a Dart web app, you need the following software:</p><ul><li><a href="https://www.google.com/chrome">Google Chrome.</a></li><li><a href="/get-dart">Dart SDK</a>, version 2.0.0 or higher.</li><li>One of the following development environments:<ul><li>Command-line: <a href="#getting-command-line-tool-packages">Dart command-line tool packages</a> such as webdev (required for both Dart and Chrome DevTools) and devtools (required for Dart DevTools).<br><em>or</em></li><li>A <a href="/tools#editors">Dart IDE or editor</a> that supports web development.</li></ul></li><li>A <a href="/web">Dart web app</a> to debug.</li></ul><div class="header-wrapper"><h2 id="using-dart-devtools">Getting started with Dart DevTools</h2><a class="heading-link" href="#using-dart-devtools" aria-label="Link to 'Getting started with Dart DevTools' section">#</a></div><img src="/assets/img/dart-devtools-screenshot.png" alt="DevTools"><p>This section leads you through the basics of using Dart DevTools to debug a web app. If you already have an app that's ready to debug, you can skip creating the test app (step 1), but you'll need to adjust the instructions to match your app.</p><ol><li><p><em>Optional:</em> Clone the <a href="https://github.com/dart-lang/webdev">webdev repo,</a> so you can use its example app to play with Dart DevTools.</p></li><li><p><em>Optional:</em> Install the <a href="https://chrome.google.com/webstore/detail/dart-debug-extension/eljbmlghnomdjgdjmbdekegdkbabckhm">Dart Debug Extension</a> so that you can run your app and open the Dart DevTools in an already-running instance of Chrome.</p></li><li><p>In your app's top directory, run <code>dart pub get</code> to get its dependencies.</p><div class="code-block-wrapper language-console"><div class="code-block-body"><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#222222">$ cd example</span></span> <span class="line"><span style="color:#222222">$ dart pub get</span></span></code></pre></div></div></li><li><p>Compile and serve the app in debug mode, using either your IDE or <code>webdev</code> at the command line.</p><aside class="alert alert-info"><div class="alert-header"><i class="material-symbols" aria-hidden="true">info</i> <span>Note</span></div><div class="alert-content"><p>The first compilation takes the longest, because the entire app must be compiled. After that, refreshes are much faster.</p></div></aside><p>If you're using webdev at the command line, the command to use depends on whether you want (or need) to run the app and debugger in an already-running instance of Chrome.</p><ul><li><p>If you have <a href="https://chrome.google.com/webstore/detail/dart-debug-extension/eljbmlghnomdjgdjmbdekegdkbabckhm">Dart Debug Extension</a> installed and want to use an existing instance of Chrome to debug:</p><div class="code-block-wrapper language-console"><div class="code-block-body"><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#222222">$ webdev serve --debug-extension</span></span></code></pre></div></div></li><li><p>Otherwise, use the following command, which launches a new instance of Chrome and runs the app:</p><div class="code-block-wrapper language-console"><div class="code-block-body"><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#222222">$ webdev serve --debug</span></span></code></pre></div></div></li></ul></li><li><p>If your app isn't already running, open it in a Chrome browser window.<br>For example, if you use <code>webdev serve --debug-extension</code> with no arguments, open <a href="http://http://127.0.0.1:8080">http://127.0.0.1:8080</a>.</p></li><li><p>Open Dart DevTools to debug the app that's running in the current window.</p><ul><li><p>If Dart Debug Extension is installed and you used the <code>--debug-extension</code> flag to <code>webdev</code>, click the Dart logo <img src="/assets/img/logo/dart-64.png" alt="Dart logo" class="align-baseline text-icon"> at the top right of the browser window.</p></li><li><p>If you used the <code>--debug</code> flag to <code>webdev</code>, press <kbd>Alt</kbd>+<kbd>D</kbd> (or <kbd>Option</kbd>+<kbd>D</kbd> on macOS).</p></li></ul><p>The Dart DevTools window comes up and displays the source code for your app's main file.</p></li><li><p>Set a breakpoint inside a timer or event handler by clicking to the left of one of its lines of code.<br>For example, click the line number for the first line inside an event handler or timer callback.</p></li><li><p>Trigger the event that causes the function call. Execution stops at the breakpoint.</p></li><li><p>In the <strong>Variables</strong> pane, inspect the values of variables.</p></li><li><p>Resume script execution, and trigger the event again or press <strong>Pause</strong>. Execution pauses again.</p></li><li><p>Try stepping through code line-by-line using the <strong>Step In</strong>, <strong>Step Over</strong>, and <strong>Step Out</strong> buttons.</p><aside class="alert alert-info"><div class="alert-header"><i class="material-symbols" aria-hidden="true">info</i> <span>Note</span></div><div class="alert-content"><p>Dart DevTools doesn't step into SDK code. For example, if you press <strong>Step In</strong> at a call to <code>print()</code>, you go to the next line, not into the SDK code that implements <code>print()</code>.</p></div></aside></li><li><p>Change your source code and reload the Chrome window that's running the app. The app quickly rebuilds and reloads. Until <a href="https://github.com/flutter/devtools/issues/1925">issue 1925</a> is fixed, you lose your breakpoints when reloading the app.</p></li><li><p>Click the <strong>Logging</strong> button to see stdout, stderr, and system logs.</p></li></ol><div class="header-wrapper"><h2 id="getting-command-line-tool-packages">Getting command-line tool packages</h2><a class="heading-link" href="#getting-command-line-tool-packages" aria-label="Link to 'Getting command-line tool packages' section">#</a></div><p>If you're using the command line instead of an IDE or Dart-enabled editor, then you need the <a href="/tools/webdev">webdev tool</a>. Dart DevTools is provided by the SDK.</p><div class="code-block-wrapper language-console"><div class="code-block-body"><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#222222">$ dart pub global activate webdev</span></span></code></pre></div></div><p>If your PATH environment variable is set up correctly, you can now use these tools at the command line:</p><div class="code-block-wrapper language-console"><div class="code-block-body"><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#222222">$ webdev --help</span></span> <span class="line"><span style="color:#222222">A tool to develop Dart web projects.</span></span> <span class="line"><span style="color:#222222">...</span></span></code></pre></div></div><p>For information on setting PATH, see the <a href="/tools/pub/cmd/pub-global"><code>dart pub global</code> documentation.</a></p><p>Whenever you update the Dart SDK, update the tools by activating them again:</p><div class="code-block-wrapper language-console"><div class="code-block-body"><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#222222">$ dart pub global activate webdev </span><span style="color:#6E6E70"># update webdev</span></span></code></pre></div></div><div class="header-wrapper"><h2 id="debugging">Debugging production code</h2><a class="heading-link" href="#debugging" aria-label="Link to 'Debugging production code' section">#</a></div><p>This section gives tips for debugging production-compiled code in Chrome, Firefox, and Safari. You can only debug JavaScript code in browsers that support source maps such as Chrome.</p><aside class="alert alert-success"><div class="alert-header"><i class="material-symbols" aria-hidden="true">lightbulb</i> <span>Tip</span></div><div class="alert-content"><p>Whenever possible, instead of debugging production code, debug code using a development server such as provided by <a href="/tools/webdev"><code>webdev</code></a>.</p></div></aside><p>Whichever browser you use, you should enable pausing on at least uncaught exceptions, and perhaps on all exceptions. For frameworks such as <code>dart:async</code> that wrap user code in try-catch, we recommend pausing on all exceptions.</p><div class="header-wrapper"><h3 id="dart2js-debugging-chrome">Chrome</h3><a class="heading-link" href="#dart2js-debugging-chrome" aria-label="Link to 'Chrome' section">#</a></div><p>To debug in Chrome:</p><ol><li>Open the Developer Tools window, as described in the <a href="https://developer.chrome.com/docs/devtools/">Chrome DevTools documentation.</a></li><li>Turn on source maps, as described in the video <a href="https://bit.ly/YugIUY">SourceMaps in Chrome.</a></li><li>Enable debugging, either on all exceptions or only on uncaught exceptions, as described in <a href="https://developer.chrome.com/docs/devtools/javascript/breakpoints/">How to set breakpoints.</a></li><li>Reload your app.</li></ol><div class="header-wrapper"><h3 id="dart2js-debugging-ie">Edge</h3><a class="heading-link" href="#dart2js-debugging-ie" aria-label="Link to 'Edge' section">#</a></div><p>To debug in Edge:</p><ol><li>Update to the latest version of Edge.</li><li>Load <strong>Developer Tools</strong> (<strong><a href="https://docs.microsoft.com/en-us/microsoft-edge/devtools-guide-chromium/landing/">F12</a></strong>).</li><li>Reload the app. The <strong>debugger</strong> tab shows source-mapped files.</li><li>Exception behavior can be controlled through <strong>Ctrl+Shift+E</strong>; the default is <strong>Break on unhandled exceptions</strong>.</li></ol><div class="header-wrapper"><h3 id="dart2js-debugging-firefox">Firefox</h3><a class="heading-link" href="#dart2js-debugging-firefox" aria-label="Link to 'Firefox' section">#</a></div><p>To debug in Firefox:</p><ol><li><p>Open the <strong>Web Developer Tools</strong> window, as described in the <a href="https://firefox-source-docs.mozilla.org/devtools-user/index.html">Firefox developer tools documentation</a>.</p></li><li><p>Enable <strong>Pause on exceptions</strong>, as shown in the following figure:</p><img width="640px" src="/assets/img/ff-debug.png" alt="Enable Pause on exceptions in Firefox debugger"></li><li><p>Reload the app. The <strong>Debugger</strong> tab shows source-mapped files.</p></li></ol><div class="header-wrapper"><h3 id="dart2js-debugging-safari">Safari</h3><a class="heading-link" href="#dart2js-debugging-safari" aria-label="Link to 'Safari' section">#</a></div><p>To debug in Safari:</p><ol><li>Turn on the <strong>Develop</strong> menu, as described in the <a href="https://developer.apple.com/library/archive/documentation/NetworkingInternetWeb/Conceptual/Web_Inspector_Tutorial/EnableWebInspector/EnableWebInspector.html">Safari Web Inspector Tutorial.</a></li><li>Enable breaks, either on all exceptions or only on uncaught exceptions. See <a href="https://support.apple.com/en-ca/guide/safari-developer/add-a-javascript-breakpoint-dev5e4caf347/mac">Add a JavaScript breakpoint</a> under <a href="https://support.apple.com/en-ca/guide/safari-developer/welcome/mac">Safari Developer Help.</a></li><li>Reload your app.</li></ol><div class="header-wrapper"><h2 id="resources">Resources</h2><a class="heading-link" href="#resources" aria-label="Link to 'Resources' section">#</a></div><p>To learn more, see the following:</p><ul><li>Documentation for <a href="/tools#editors">your IDE</a></li><li><a href="/tools/dart-devtools">Dart DevTools documentation</a></li><li><a href="/tools/webdev">webdev tool documentation</a></li><li><a href="https://pub.dev/packages/webdev">webdev package documentation</a></li></ul><p id="page-github-links"><span>Unless stated otherwise, the documentation on this site reflects Dart 3.5.4. Page last updated on 2024-05-29.</span> <a href="https://github.com/dart-lang/site-www/tree/main/src/content/web/debugging.md" target="_blank" rel="noopener">View source</a> <span>or </span><a href="https://github.com/dart-lang/site-www/issues/new?template=1_page_issue.yml&page-url=https://dart.dev/web/debugging/&page-source=https://github.com/dart-lang/site-www/tree/main/src/content/web/debugging.md" title="Report an issue with this page" target="_blank" rel="noopener">report an issue</a>.</p></div></article></main><footer id="page-footer"><div class="footer-section footer-main"><a href="/" class="brand" title="Dart"><img src="/assets/img/logo/logo-white-text.svg" alt="Dart" width="164"></a><div class="footer-social-links"><a href="https://medium.com/dartlang" target="_blank" rel="noopener" title="Medium blog"><svg><use href="/assets/img/social/medium.svg#medium"></use></svg> </a><a href="https://github.com/dart-lang" target="_blank" rel="noopener" title="GitHub"><svg><use href="/assets/img/social/github.svg#github"></use></svg> </a><a href="https://twitter.com/dart_lang" target="_blank" rel="noopener" title="X (Twitter)"><svg><use href="/assets/img/social/x.svg#x"></use></svg></a></div></div><div class="footer-section footer-tray"><div class="footer-licenses">Except as otherwise noted, this site is licensed under a <a href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>, and code samples are licensed under the <a href="https://opensource.org/licenses/BSD-3-Clause">3-Clause BSD License</a>.</div><div class="footer-utility-links"><ul><li><a href="/terms" title="Terms of use">Terms</a></li><li><a href="https://policies.google.com/privacy" target="_blank" rel="noopener" title="Privacy policy">Privacy</a></li><li><a href="/security" title="Security philosophy and practices">Security</a></li></ul></div></div></footer></body></html>