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type="application/ld+json">{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Tutorial","item":"https://id.javascript.info/"},{"@type":"ListItem","position":2,"name":"Bahasa JavaScript","item":"https://id.javascript.info/js"},{"@type":"ListItem","position":3,"name":"Miscellaneous","item":"https://id.javascript.info/js-misc"}]}</script></ol><div class="updated-at" data-tooltip="Terakhir diperbarui pada 7 Oktober 2020"><div class="updated-at__content">7 Oktober 2020</div></div></div><h1 class="main__header-title">Eval: menjalankan kode dari _string_</h1></div></header><div class="content"><article class="formatted" itemscope itemtype="http://schema.org/TechArticle"><meta itemprop="name" content="Eval: menjalankan kode dari _string_"><div itemprop="author" itemscope itemtype="http://schema.org/Person"><meta itemprop="email" content="iliakan@gmail.com"><meta itemprop="name" content="Ilya Kantor"></div><div itemprop="articleBody"><p>Fungsi bawaan <code>eval</code> memungkinkan kita untuk menjalankan kode dari sebuah <em>string</em>.</p> <p>Sintaksnya adalah:</p> <div id="tfjyx6pp81" data-trusted="1" class="code-example"> <div class="codebox code-example__codebox"> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>let result = eval(code);</code></pre> </div> </div> </div><p>Sebagai contoh:</p> <div id="8ewzqcs5nr" data-trusted="1" class="code-example"> <div class="codebox code-example__codebox"> <div class="toolbar codebox__toolbar"> <div class="toolbar__tool"> <a href="#" title="jalankan" data-action="run" class="toolbar__button toolbar__button_run"></a> </div> <div class="toolbar__tool"> <a href="#" title="buka pada sandbox" target="_blank" data-action="edit" class="toolbar__button toolbar__button_edit"></a> </div> </div> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>let code = 'alert("Halo")'; eval(code); // Halo</code></pre> </div> </div> </div><p>Sebuah kode yang berupa <em>string</em> bisa panjang, berupa deklarasi fungsi, variabel dan lain-lain.</p> <p>Hasil dari <code>eval</code> adalah hasil dari peryataan terakhir.</p> <p>Sebagai contoh:</p> <div id="uf3aysjeji" data-trusted="1" class="code-example"> <div class="codebox code-example__codebox"> <div class="toolbar codebox__toolbar"> <div class="toolbar__tool"> <a href="#" title="jalankan" data-action="run" class="toolbar__button toolbar__button_run"></a> </div> <div class="toolbar__tool"> <a href="#" title="buka pada sandbox" target="_blank" data-action="edit" class="toolbar__button toolbar__button_edit"></a> </div> </div> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>let value = eval('1+1'); alert(value); // 2</code></pre> </div> </div> </div><div id="em3ai83zvk" data-trusted="1" class="code-example"> <div class="codebox code-example__codebox"> <div class="toolbar codebox__toolbar"> <div class="toolbar__tool"> <a href="#" title="jalankan" data-action="run" class="toolbar__button toolbar__button_run"></a> </div> <div class="toolbar__tool"> <a href="#" title="buka pada sandbox" target="_blank" data-action="edit" class="toolbar__button toolbar__button_edit"></a> </div> </div> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>let value = eval('let i = 0; ++i'); alert(value); // 1</code></pre> </div> </div> </div><p>Kode yang dievaluasi akan dieksekusi di lingkungan leksikal saat ini, sehingga dapat melihat variabel luar:</p> <div id="u6sj2siir1" data-trusted="1" class="code-example" data-highlight="[{"start":5,"end":5}]"> <div class="codebox code-example__codebox"> <div class="toolbar codebox__toolbar"> <div class="toolbar__tool"> <a href="#" title="jalankan" data-action="run" class="toolbar__button toolbar__button_run"></a> </div> <div class="toolbar__tool"> <a href="#" title="buka pada sandbox" target="_blank" data-action="edit" class="toolbar__button toolbar__button_edit"></a> </div> </div> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>let a = 1; function f() { let a = 2; eval('alert(a)'); // 2 } f();</code></pre> </div> </div> </div><p>Itu juga dapat mengubah variabel luar:</p> <div id="8l2gom2u61" data-trusted="0" class="code-example" data-refresh="1"> <div class="codebox code-example__codebox"> <div class="toolbar codebox__toolbar"> <div class="toolbar__tool"> <a href="#" title="jalankan" data-action="run" class="toolbar__button toolbar__button_run"></a> </div> <div class="toolbar__tool"> <a href="#" title="buka pada sandbox" target="_blank" data-action="edit" class="toolbar__button toolbar__button_edit"></a> </div> </div> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>let x = 5; eval("x = 10"); alert(x); // 10, nilai diubah</code></pre> </div> </div> </div><p>Dalam mode ketat, <code>eval</code> memiliki lingkungan leksikal sendiri. Jadi, fungsi dan variabel yang dideklarasikan di dalam eval, tidak akan terlihat di luar:</p> <div id="d44sh1a310" data-trusted="0" class="code-example" data-refresh="1"> <div class="codebox code-example__codebox"> <div class="toolbar codebox__toolbar"> <div class="toolbar__tool"> <a href="#" title="jalankan" data-action="run" class="toolbar__button toolbar__button_run"></a> </div> <div class="toolbar__tool"> <a href="#" title="buka pada sandbox" target="_blank" data-action="edit" class="toolbar__button toolbar__button_edit"></a> </div> </div> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>// pengingat: dalam contoh yang dijalankan 'use strict' diaktifkan secara bawaan eval("let x = 5; function f() {}"); alert(typeof x); // undefined (tidak ada variabel) // fungsi f juga tidak terlihat</code></pre> </div> </div> </div><p>Tanpa <code>use strict</code>, <code>eval</code> tidak memiliki lingkungan leksikal sendiri, jadi kita akan melihat <code>x</code> dan <code>f</code> di luar.</p> <h2><a class="main__anchor" name="menggunakan-eval" href="#menggunakan-eval">Menggunakan “eval”</a></h2><p>Dalam pemrograman modern <code>eval</code> jarang digunakan. Sering dikatakan bahwa “<em>eval is evil</em>” atau “<code>eval</code> itu jahat”.</p> <p>Alasannya sederhana: dulu JavaScript adalah bahasa yang jauh lebih lemah, banyak hal yang hanya bisa dilakukan dengan <code>eval</code>. Tapi waktu itu telah berlalu satu dekade yang lalu.</p> <p>Sekarang, hampir tidak ada alasan untuk menggunakan <code>eval</code>. Jika seseorang menggunakannya, ada kemungkinan mereka dapat menggantinya dengan konstruksi bahasa modern atau <a href="/modules">JavaScript Module</a>.</p> <p>Harap dicatat bahwa kemampuannya untuk mengakses variabel luar memiliki efek samping.</p> <p><em>Code minifiers</em> (alat yang digunakan sebelum JS masuk ke produksi, untuk mengkompresnya) mengubah nama variabel lokal menjadi lebih pendek (seperti <code>a</code>, <code>b</code> dll) untuk membuat kode menjadi lebih kecil. Biasanya itu aman, tetapi tidak jika <code>eval</code> digunakan, karena variabel lokal dapat diakses dari kode yang dievaluasi dari <em>string</em>. Jadi <em>minifiers</em> tidak melakukan itu untuk mengganti nama semua variabel yang terlihat dari <code>eval</code>. Itu berdampak negatif pada rasio kompresi kode.</p> <p>Menggunakan variabel lokal luar di dalam <code>eval</code> juga dianggap sebagai praktik pemrograman yang buruk, karena membuat kode lebih sulit dipertahankan.</p> <p>Ada dua cara untuk terhindar dan aman dari masalah seperti itu.</p> <p><strong>Jika kode yang dievaluasi tidak menggunakan variabel luar, panggil <code>eval</code> sebagai <code>window.eval(...)</code>:</strong></p> <p>Dengan cara ini, kode akan dijalankan dalam lingkup global:</p> <div id="0ak4ieml4f" data-trusted="0" class="code-example" data-refresh="1"> <div class="codebox code-example__codebox"> <div class="toolbar codebox__toolbar"> <div class="toolbar__tool"> <a href="#" title="jalankan" data-action="run" class="toolbar__button toolbar__button_run"></a> </div> <div class="toolbar__tool"> <a href="#" title="buka pada sandbox" target="_blank" data-action="edit" class="toolbar__button toolbar__button_edit"></a> </div> </div> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>let x = 1; { let x = 5; window.eval('alert(x)'); // 1 (variabel global) }</code></pre> </div> </div> </div><p><strong>Jika kode yang dievaluasi membutuhkan variabel lokal, ubah <code>eval</code> menjadi <code>new Function</code> dan teruskan sebagai argumen:</strong></p> <div id="nm97c92tqi" data-trusted="1" class="code-example"> <div class="codebox code-example__codebox"> <div class="toolbar codebox__toolbar"> <div class="toolbar__tool"> <a href="#" title="jalankan" data-action="run" class="toolbar__button toolbar__button_run"></a> </div> <div class="toolbar__tool"> <a href="#" title="buka pada sandbox" target="_blank" data-action="edit" class="toolbar__button toolbar__button_edit"></a> </div> </div> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>let f = new Function('a', 'alert(a)'); f(5); // 5</code></pre> </div> </div> </div><p>Konstruksi <code>new Function</code> dijelaskan dalam bab <a href="/new-function">Sintaks "new Function"</a>. Itu membuat fungsi baru dari sebuah <em>string</em> dan juga dalam lingkup global. Jadi tidak bisa melihat variabel lokal. Tetapi jauh lebih jelas jika meneruskannya sebagai argumen secara eksplisit, seperti pada contoh di atas.</p> <h2><a class="main__anchor" name="ringkasan" href="#ringkasan">Ringkasan</a></h2><p>Pemanggilan <code>eval(code)</code> menjalankan kode dari sebuah <em>string</em> dan mengembalikan hasil dari pernyataan terakhir.</p> <ul> <li>Jarang digunakan dalam JavaScript modern, karena biasanya tidak diperlukan.</li> <li>Dapat mengakses variabel lokal luar. Itu dianggap praktik yang buruk.</li> <li>Sebaga gantinya, untuk <code>eval</code> sebuah kode dalam lingkup global, gunakan <code>window.eval(code)</code>.</li> <li>Atau, jika kode Anda memerlukan beberapa data dari cakupan luar, gunakan <code>new Function</code> dan teruskan sebagai argumen.</li> </ul> </div></article><div class="tasks formatted"><h2 class="tasks__title" id="tasks"><a class="tasks__title-anchor main__anchor main__anchor main__anchor_noicon" href="#tasks">Tugas</a></h2><div class="task tasks__task"><div class="task__header"><div class="task__title-wrap"><h3 class="task__title"><a class="main__anchor" href="#kalkulator-eval" name="kalkulator-eval">Kalkulator-_eval_</a></h3><a class="task__open-link" href="/task/eval-calculator" target="_blank"></a></div><div class="task__header-note"><span class="task__importance" title="Seberapa penting tugas itu, dari 1 hingga 5">pentingnya: 4</span></div><div class="task__content"><div class="task__formatted"><p>Buatlah kalkulator yang meminta operasi aritmatika dan mengembalikan hasilnya.</p> <p>Tidak perlu memeriksa kebenaran operasi dalam tugas ini. Cukup evaluasi dan kembalikan hasilnya.</p> <p><a href="#" onclick="event.preventDefault(); runDemo(this)">jalankan demonya</a></p></div><button class="task__solution" type="button">solusi</button><div class="task__answer"><div class="task__answer-content"><div class="formatted"><p>Mari gunakan <code>eval</code> untuk menghitung rumus matematika:</p> <div id="i9g1m4hjhq" data-trusted="1" class="code-example" data-demo="1"> <div class="codebox code-example__codebox"> <div class="toolbar codebox__toolbar"> <div class="toolbar__tool"> <a href="#" title="jalankan" data-action="run" class="toolbar__button toolbar__button_run"></a> </div> <div class="toolbar__tool"> <a href="#" title="buka pada sandbox" target="_blank" data-action="edit" class="toolbar__button toolbar__button_edit"></a> </div> </div> <div class="codebox__code" data-code="1"> <pre class="line-numbers language-javascript"><code>let expr = prompt("Type an arithmetic expression?", '2*3+2'); alert( eval(expr) );</code></pre> </div> </div> </div><p>Pengguna dapat memasukkan teks atau kode apa pun.</p> <p>Untuk membuat semuanya aman dan membatasinya hanya untuk operasi aritmatika, kita dapat memeriksa <code>expr</code> menggunakan <a href="/regular-expressions"><em>regular expression</em></a>, sehingga hanya dapat berisi angka dan operator.</p> </div></div><button class="close-button task__answer-close" type="button" title="tutup"></button></div></div></div></div></div></div><div class="page__nav-wrap"><a class="page__nav page__nav_prev" href="/proxy" data-tooltip="Proxy and Reflect"><span class="page__nav-text"><span class="page__nav-text-shortcut"></span></span><span class="page__nav-text-alternate">Pelajaran sebelumnya</span></a><a class="page__nav page__nav_next" href="/currying-partials" data-tooltip="_Currying_"><span class="page__nav-text"><span class="page__nav-text-shortcut"></span></span><span class="page__nav-text-alternate">Pelajaran berikutnya</span></a></div><div class="article-tablet-foot tablet-only"><div class="article-tablet-foot__layout"><div class="share-icons"><span class="share-icons__title">Bagikan</span><a class="share share_tw" href="https://twitter.com/share?url=https%3A%2F%2Fid.javascript.info%2Feval" rel="nofollow"></a><a class="share share_fb" href="https://www.facebook.com/sharer/sharer.php?s=100&p%5Burl%5D=https%3A%2F%2Fid.javascript.info%2Feval" rel="nofollow"></a></div><div class="article-tablet-foot__map"><a class="map" href="/tutorial/map" data-action="tutorial-map"><span class="map__text">Peta tutorial</span></a></div></div></div><div class="comments formatted" id="comments"><div class="comments__header"><h2 class="comments__header-title"><a href="#comments" name="comments">komentar</a></h2><div class="comments__read-before"><span class="comments__read-before-link">baca ini sebelum berkomentar…</span><div class="comments__read-before-popup"><div class="comments__read-before-popup-i"><ul><li>Jika Anda memiliki saran apa yang harus ditingkatkan - silakan kunjungi <a href="https://github.com/javascript-tutorial/en.javascript.info/issues/new">kirimkan Github issue</a> atau pull request sebagai gantinya berkomentar.</li><li>Jika Anda tidak dapat memahami sesuatu dalam artikel – harap jelaskan.</li><li>Untuk menyisipkan beberapa kata kode, gunakan tag <code><code></code>, untuk beberapa baris – bungkus dengan tag <code><pre></code>, untuk lebih dari 10 baris – gunakan sandbox (<a href='https://plnkr.co/edit/?p=preview'>plnkr</a>, <a href='https://jsbin.com'>jsbin</a>, < a href='http://codepen.io'>codepen</a>…)</li></ul></div></div></div></div><div id="disqus_thread"></div><script>var disqus_config = function() { if (!this.page) this.page = {}; 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