path: root/files/zh-tw/web/javascript/reference/global_objects/bigint/index.html

---
title: BigInt
slug: Web/JavaScript/Reference/Global_Objects/BigInt
translation_of: Web/JavaScript/Reference/Global_Objects/BigInt
---
<p>{{JSRef}}{{SeeCompatTable}}</p>

<p><code>BigInt</code> 是一個內建的物件，提供了表示大於2^53的整數的功能 (2^53是JavaScript原生的{{JSxRef("Number")}}能夠表示的最大值)</p>

<h2 id="語法">語法</h2>

<pre class="brush: js">BigInt(value);
</pre>

<h3 id="參數">參數</h3>

<dl>
 <dt><code>value</code></dt>
 <dd>欲創建的數值，可以為整數或字串。</dd>
</dl>

<div class="notecard note">
<p><strong>Note:</strong> <code>BigInt()</code> 不和 {{JSxRef("Operators/new", "new")}} 一起使用。</p>
</div>

<dl>
</dl>

<h2 id="說明">說明</h2>

<p><code>BigInt</code> 是透過在一個數值後加上 <code>n</code> ，例如 <code>10n</code> ，或呼叫 <code>BigInt()</code> 所生成的。</p>

<pre class="brush: js">const theBiggestInt = 9007199254740991n;

const alsoHuge = BigInt(9007199254740991);
// ↪ 9007199254740991n

const hugeString = BigInt("9007199254740991");
// ↪ 9007199254740991n

const hugeHex = BigInt("0x1fffffffffffff");
// ↪ 9007199254740991n

const hugeBin = BigInt("0b11111111111111111111111111111111111111111111111111111");
// ↪ 9007199254740991n
</pre>

<p><code>BigInt</code> 跟 {{JSxRef("Number")}} 很像，但在某些部分有些許不同 — 它不可以被用在內建的 {{JSxRef("Math")}} 物件方法中、而且不可以跟 <code>Number</code> 的實體混用運算子。</p>

<div class="notecard warning">
<p><strong>警告：</strong> {{JSxRef("Number")}} 和 <code>BigInt</code> 不能混和計算 — 他們必須被轉換到同一個型態。</p>

<p>然而，在相互轉換時要注意， <code>BigInt</code> 在被轉換成 <code>Number</code> 時可能會遺失部分精度的資訊。</p>
</div>

<h3 id="類別資訊">類別資訊</h3>

<p>當使用 <code>typeof</code> 測試時，一個 <code>BigInt</code> 會回傳 "bigint"：</p>

<pre class="brush: js">typeof 1n === 'bigint'; // true
typeof BigInt('1') === 'bigint'; // true
</pre>

<p>當使用 <code>Object</code> 來包裹時，<code>BigInt</code> 會被看成是普通的 "object" 型態：</p>

<pre class="brush: js">typeof Object(1n) === 'object'; // true
</pre>

<h3 id="Operators">Operators</h3>

<p>下列的運算子可以被用在 <code>BigInt</code> 上 (或由object包裹的 <code>BigInt</code>): <code>+</code>, <code>*</code>, <code>-</code>, <code>**</code>, <code>%</code>.</p>

<pre class="brush: js">const previousMaxSafe = BigInt(Number.MAX_SAFE_INTEGER);
// ↪ 9007199254740991

const maxPlusOne = previousMaxSafe + 1n;
// ↪ 9007199254740992n

const theFuture = previousMaxSafe + 2n;
// ↪ 9007199254740993n, this works now!

const multi = previousMaxSafe * 2n;
// ↪ 18014398509481982n

const subtr = multi – 10n;
// ↪ 18014398509481972n

const mod = multi % 10n;
// ↪ 2n

const bigN = 2n ** 54n;
// ↪ 18014398509481984n

bigN * -1n
// ↪ –18014398509481984n
</pre>

<p><code>/</code> 運算子也同樣的能夠運行。然而，因為型態是 <code>BigInt</code> 而不是 <code>BigDecimal</code> ，除法運算會無條件捨去小數。也就是說，回傳值不會包含小數部分。</p>

<div class="notecard warning">
<p><strong>警告：</strong>回傳值帶小數的運算在使用<code>BigInt</code> 時小數部分會被捨去。</p>
</div>

<pre class="brush: js">const expected = 4n / 2n;
// ↪ 2n

const rounded = 5n / 2n;
// ↪ 2n, not 2.5n

</pre>

<h3 id="比較">比較</h3>

<p>一個 <code>BigInt</code> 並不嚴格等於一個 {{JSxRef("Global_Objects/Number", "Number")}}，但他們會一般相等。</p>

<pre class="brush: js">0n === 0
// ↪ false

0n == 0
// ↪ true</pre>

<p>一個 {{JSxRef("Global_Objects/Number", "Number")}} 和 <code>BigInt</code> 可以像普通運算一樣比較。</p>

<pre class="brush: js">1n &lt; 2
// ↪ true

2n &gt; 1
// ↪ true

2 &gt; 2
// ↪ false

2n &gt; 2
// ↪ false

2n &gt;= 2
// ↪ true</pre>

<p>他們可以參雜在陣列中並照預期的被排序。</p>

<pre class="brush: js">const mixed = [4n, 6, -12n, 10, 4, 0, 0n];
// ↪  [4n, 6, -12n, 10, 4, 0, 0n]

mixed.sort();
// ↪ [-12n, 0, 0n, 10, 4n, 4, 6]
</pre>

<p>Note that comparisons with <code>Object</code>-wrapped <code>BigInt</code>s act as with other objects, only indicating equality when the same object instance is compared:</p>

<pre class="brush: js">0n === Object(0n); // false
Object(0n) === Object(0n); // false

const o = Object(0n);
o === o // true
</pre>

<h3 id="Conditionals">Conditionals</h3>

<p>A <code>BigInt</code> behaves like a {{JSxRef("Global_Objects/Number", "Number")}} in cases where it is converted to a {{JSxRef("Global_Objects/Boolean", "Boolean")}}: via the {{JSxRef("Global_Objects/Boolean", "Boolean")}} function; when used with logical operators {{JSxRef("Operators/Logical_Operators", "Logical Operators")}} <code>||</code>, <code>&amp;&amp;</code>, and <code>!</code>; or within a conditional test like an {{JSxRef("Statements/if...else", "if statement")}}.</p>

<pre class="brush: js">if (0n) {
  console.log('Hello from the if!');
} else {
  console.log('Hello from the else!');
}

// ↪ "Hello from the else!"

0n || 12n
// ↪ 12n

0n &amp;&amp; 12n
// ↪ 0n

Boolean(0n)
// ↪ false

Boolean(12n)
// ↪ true

!12n
// ↪ false

!0n
// ↪ true
</pre>

<h2 id="方法">方法</h2>

<dl>
 <dt>{{JSxRef("BigInt.asIntN()")}}</dt>
 <dd>Clamps a BigInt value to a signed integer value, and returns that value.</dd>
 <dt>{{JSxRef("BigInt.asUintN()")}}</dt>
 <dd>Clamps a BigInt value to an unsigned integer value, and returns that value.</dd>
</dl>

<h2 id="屬性">屬性</h2>

<dl>
 <dt>{{JSxRef("BigInt.prototype")}}</dt>
 <dd>允許對一個 <code>BigInt</code> 物件增加其屬性。</dd>
</dl>

<h2 id="BigInt_物件實體"><code>BigInt</code> 物件實體</h2>

<p>All <code>BigInt</code> instances inherit from <code>BigInt.prototype</code>. The prototype object of the <code>BigInt</code> constructor can be modified to affect all <code>BigInt</code> instances.</p>

<h3 id="方法_2">方法</h3>

<p>{{page("/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt/prototype", "Methods")}}</p>

<h2 id="建議用法">建議用法</h2>

<h3 id="轉型">轉型</h3>

<p>因為在 {{JSxRef("Global_Objects/Number", "Number")}} 和 <code>BigInt</code> 之間轉換可能造成精度遺失，建議當數值會超過2^53時只使用 <code>BigInt</code> ，而不要在兩者之間進行轉換。</p>

<h3 id="加密">加密</h3>

<p><code>BigInt</code> 支援的運算並非常數時間。因此 <code>BigInt</code> <a href="https://www.chosenplaintext.ca/articles/beginners-guide-constant-time-cryptography.html">不適用在加密學上</a>。</p>

<h2 id="範例">範例</h2>

<h3 id="計算質數">計算質數</h3>

<pre class="brush: js">function isPrime(p) {
  for (let i = 2n; i * i &lt;= p; i++) {
    if (p % i === 0n) return false;
  }
  return true;
}

// Takes a BigInt as an argument and returns a BigInt
function nthPrime(nth) {
  let maybePrime = 2n;
  let prime = 0n;

  while (nth &gt;= 0n) {
    if (isPrime(maybePrime)) {
      nth -= 1n;
      prime = maybePrime;
    }
    maybePrime += 1n;
  }

  return prime;
}

nthPrime(20n)
// ↪ 73n</pre>

<h2 id="規範">規範</h2>

{{Specifications}}

<h2 id="瀏覽器相容性">瀏覽器相容性</h2>

{{Compat}}

<h2 id="另見">另見</h2>

<ul>
 <li>{{JSxRef("Number")}}</li>
</ul>