---
title: Math.log2()
slug: Web/JavaScript/Reference/Global_Objects/Math/log2
translation_of: Web/JavaScript/Reference/Global_Objects/Math/log2
---
<div>{{JSRef}}</div>

<p> <strong><code>Math.log2()</code></strong> 함수는 숫자를 log<sub>2</sub>(숫자)로 반환합니다.</p>

<p><math display="block"><semantics><mrow><mo>∀</mo><mi>x</mi><mo>&gt;</mo><mn>0</mn><mo>,</mo><mstyle mathvariant="monospace"><mrow><mo lspace="0em" rspace="thinmathspace">Math.log2</mo><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow></mstyle><mo>=</mo><msub><mo lspace="0em" rspace="0em">log</mo><mn>2</mn></msub><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo><mo>=</mo><mtext>the unique</mtext><mspace width="thickmathspace"></mspace><mi>y</mi><mspace width="thickmathspace"></mspace><mtext>such that</mtext><mspace width="thickmathspace"></mspace><msup><mn>2</mn><mi>y</mi></msup><mo>=</mo><mi>x</mi></mrow><annotation encoding="TeX">\forall x &gt; 0, \mathtt{\operatorname{Math.log2}(x)} = \log_2(x) = \text{the unique} \; y \; \text{such that} \; 2^y = x</annotation></semantics></math></p>

<h2 id="문법">문법</h2>

<pre class="syntaxbox"><code>Math.log2(<var>x</var>)</code></pre>

<h3 id="매개변수">매개변수</h3>

<dl>
 <dt><code>x</code></dt>
 <dd>숫자.</dd>
</dl>

<h3 id="반환_값">반환 값</h3>

<p>주어진 숫자는 log<sub>2</sub>(숫자)로 계산합니다. 만약 숫자가 음수라면 {{jsxref("NaN")}}를 반환합니다.</p>

<h2 id="설명">설명</h2>

<p>만약 <code>x</code> 의 값이 0보다 작다면(음수) 값은 항상 {{jsxref("NaN")}}로 반환합니다.</p>

<p><code>log<sub>2</sub>()</code>는 <code>Math</code>의 정적 메서드이므로 만든 <code>Math</code> 객체의 메서드가 아니라 항상 <code>Math.log2()</code>함수를 사용해야합니다. (<code>Math</code>는 생성자가 없습니다.)</p>

<p>이 함수는 Math.log(x) / Math.log(2)와 같습니다.</p>

<p>따라서 log<sub>2</sub>(e)는 {{jsxref("Math.LOG2E")}}와 같습니다. </p>

<p>그리고 위 함수는 1 / {{jsxref("Math.LN2")}}과 같습니다.</p>

<h2 id="예제">예제</h2>

<h3 id="Math.log2()"><code>Math.log2()</code></h3>

<pre class="brush: js">Math.log2(3);    // 1.584962500721156
Math.log2(2);    // 1
Math.log2(1);    // 0
Math.log2(0);    // -Infinity
Math.log2(-2);   // NaN
Math.log2(1024); // 10
</pre>

<h2 id="Polyfill">Polyfill</h2>

<p>This Polyfill emulates the <code>Math.log2</code> function. Note that it returns imprecise values on some inputs (like 1 &lt;&lt; 29), wrap into {{jsxref("Math.round()")}} if working with bit masks.</p>

<pre class="brush: js">Math.log2 = Math.log2 || function(x) {
  return Math.log(x) * Math.LOG2E;
};
</pre>

<h2 id="표준">표준</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">표준</th>
   <th scope="col">상태</th>
   <th scope="col">비고</th>
  </tr>
  <tr>
   <td>{{SpecName('ES2015', '#sec-math.log2', 'Math.log2')}}</td>
   <td>{{Spec2('ES2015')}}</td>
   <td>Initial definition.</td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-math.log2', 'Math.log2')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td> </td>
  </tr>
 </tbody>
</table>

<h2 id="브라우저_호환성">브라우저 호환성</h2>

<p>{{Compat("javascript.builtins.Math.log2")}}</p>

<h2 id="참조">참조</h2>

<ul>
 <li>{{jsxref("Math.exp()")}}</li>
 <li>{{jsxref("Math.log()")}}</li>
 <li>{{jsxref("Math.log10()")}}</li>
 <li>{{jsxref("Math.log1p()")}}</li>
 <li>{{jsxref("Math.pow()")}}</li>
</ul>