JavaScript Map keys() Method

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for (const x of fruits.keys()) { text += x; } </pre> <p class="tiy"><a target="_blank" href="/tiy/t.html?f=jsref_map_keys">Try it yourself</a></p> <div class="note"> <h3>Object as key</h3> <p class="note"><span>Note:</span>The ability to use objects as keys is an important feature of Map.</p> </div> <h3>Example 2</h3> <pre class="language-js"> // Create objects const apples = {name: 'Apples'}; const bananas = {name: 'Bananas'}; const oranges = {name: 'Oranges'}; // Create a Map const fruits = new Map(); // Add new elements to the Map fruits.set(apples, 500); fruits.set(bananas, 300); fruits.set(oranges, 200); </pre> <p class="tiy"><a target="_blank" href="/tiy/t.html?f=jsref_map_create_objects">Try it yourself</a></p> <p class="important"><span>Remember:</span>The key is an object (apples), not a string ("apples"):</p> <h3>Example 3</h3> <pre class="language-js"> fruits.get("apples"); // Returns undefined </pre> <p class="tiy"><a target="_blank" href="/tiy/t.html?f=jsref_map_get_undefined">Try it yourself</a></p> </section> <section> <h2>Syntax</h2> <pre class="language-js"> map.keys() </pre> <h3>Parameters</h3> <p>None.</p> <h3>Return value</h3> <table class="technical-details"> <tr> <th style="width: 25%;">Type</th> <th>Description</th> </tr> <tr> <td>Iterator</td> <td>An iterable object containing all keys of the Map.</td> </tr> </table> </section> <section> <h2>Browser support</h2> <p><code>map.keys()</code> Is a feature of ECMAScript6 (ES6).</p> <p>Starting from June 2017, all modern browsers support ES6 (JavaScript 2015):</p> <table class="browser-support"> <tr> <th class="bsChrome">Chrome</th> <th class="bsEdge">Edge</th> <th class="bsFirefox">Firefox</th> <th class="bsSafari">Safari</th> <th class="bsOpera">Opera</th> </tr> <tr> <td>Chrome 51</td> <td>Edge 15</td> <td>Firefox 54</td> <td>Safari 10</td> <td>Opera 38</td> </tr> <tr> <td>May 2016</td> <td>April 2017</td> <td>June 2017</td> <td>September 2016</td> <td>June 2016</td> </tr> </table> <p><code>map.keys()</code> Not Supported in Internet Explorer.</p> </section> <section class="related-pages"> <h2>Related Pages</h2> <p>Tutorial:<a href="/js/js_maps.html" title="">JavaScript Map</a></p> <p>Tutorial:<a href="/js/js_iterables.html" title="">JavaScript Iterable Objects</a></p> <p>Reference:<a href="/jsref/jsref_obj_map.html" title="">JavaScript Map</a></p> </section> <div class="prenextnav-ref"> <ul> <li> Previous Page <a href="/jsref/jsref_map_has.html" title="JavaScript Map has() Method">has()</a></li> <li> Next Page <a href="/jsref/jsref_map_set.html" title="JavaScript Map set() Method">set()</a></li> <li> Go to the Previous Level <a href="/jsref/jsref_obj_map.html" title="JavaScript Map Reference Manual">JavaScript Map Reference Manual</a></li> </ul> </div><div style="background-color:#fcfdf8; 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