Revision 1109575 of Object.is()

<div>{{JSRef}}</div>

<p>The <code><strong>Object.is()</strong></code> method determines whether two values are <a href="/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness">the same value</a>.</p>

<h2 id="Syntax">Syntax</h2>

<pre class="syntaxbox">
<code>Object.is(<var>value1</var>, <var>value2</var>);</code></pre>

<h3 id="Parameters">Parameters</h3>

<dl>
 <dt><code>value1</code></dt>
 <dd>The first value to compare.</dd>
 <dt><code>value2</code></dt>
 <dd>The second value to compare.</dd>
</dl>

<h3 id="Return_value">Return value</h3>

<p>A {{jsxref("Boolean")}} indicating whether or not the two arguments are the same value.</p>

<h2 id="Description">Description</h2>

<p><code>Object.is()</code> determines whether two values are <a href="/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness">the same value</a>. Two values are the same if one of the following holds:</p>

<ul>
 <li>both {{jsxref("undefined")}}</li>
 <li>both {{jsxref("null")}}</li>
 <li>both <code>true</code> or both <code>false</code></li>
 <li>both strings of the same length with the same characters</li>
 <li>both the same object</li>
 <li>both numbers and
  <ul>
   <li>both <code>+0</code></li>
   <li>both <code>-0</code></li>
   <li>both {{jsxref("NaN")}}</li>
   <li>or both non-zero and both not {{jsxref("NaN")}} and both have the same value</li>
  </ul>
 </li>
</ul>

<p>This is <em>not</em> the same as being equal according to the {{jsxref("Operators/Comparison_Operators", "==", "#Equality")}} operator. The {{jsxref("Operators/Comparison_Operators", "==", "#Equality")}} operator applies various coercions to both sides (if they are not the same Type) before testing for equality (resulting in such behavior as <code>"" == false</code> being <code>true</code>), but <code>Object.is</code> doesn't coerce either value.</p>

<p>This is also <em>not</em> the same as being equal according to the {{jsxref("Operators/Comparison_Operators", "===", "#Identity")}} operator. The {{jsxref("Operators/Comparison_Operators", "===", "#Identity")}} operator (and the {{jsxref("Operators/Comparison_Operators", "==", "#Equality")}} operator as well) treats the number values <code>-0</code> and <code>+0</code> as equal and treats {{jsxref("Number.NaN")}} as not equal to {{jsxref("NaN")}}.</p>

<h2 id="Examples">Examples</h2>

<pre class="brush: js">
Object.is('foo', 'foo');     // true
Object.is(window, window);   // true

Object.is('foo', 'bar');     // false
Object.is([], []);           // false

var test = { a: 1 };
Object.is(test, test);       // true

Object.is(null, null);       // true

// Special Cases
Object.is(0, -0);            // false
Object.is(-0, -0);           // true
Object.is(NaN, 0/0);         // true
</pre>

<h2 id="Polyfill_for_non-ES6_browsers">Polyfill for non-ES6 browsers</h2>

<p><code>Object.is()</code> is a proposed addition to the ECMA-262 standard; as such it may not be present in all browsers. You can work around this by using the following code at the beginning of your scripts. This will allow you to use <code>Object.is()</code> when there is no built–in support.</p>

<pre class="brush: js">
if (!Object.is) {
  Object.is = function(x, y) {
&nbsp;   // SameValue algorithm
    if (x === y) { // Steps 1-5, 7-10
&nbsp;     // Steps 6.b-6.e: +0 != -0
      return x !== 0 || 1 / x === 1 / y;
&nbsp;   } else {
&nbsp;     // Step 6.a: NaN == NaN
&nbsp;     return x !== x &amp;&amp; y !== y;
&nbsp;   }
  };
}
</pre>

<h2 id="Specifications">Specifications</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-object.is', 'Object.is')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>Initial definition.</td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-object.is', 'Object.is')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td>&nbsp;</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</h2>

<div>{{CompatibilityTable}}</div>

<div id="compat-desktop">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Chrome</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatChrome("30")}}</td>
   <td>{{CompatGeckoDesktop("22")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatSafari("9")}}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Chrome for Android</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatUnknown}}</td>
   <td>{{CompatGeckoMobile("22")}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatNo}}</td>
   <td>{{CompatSafariMobile("9")}}</td>
  </tr>
 </tbody>
</table>
</div>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness">Equality comparisons and sameness</a> — a comparison of all three built-in sameness facilities</li>
</ul>