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+---
+title: 方法定義
+slug: Web/JavaScript/Reference/Functions/Method_definitions
+translation_of: Web/JavaScript/Reference/Functions/Method_definitions
+---
+<div>{{JsSidebar("Functions")}}</div>
+
+<p>自 ECMAScript 2015 開始，引入了一種於物件初始器（objects initializers）中定義方法的簡短語法。是一個將函式指派予方法名稱的簡便方式。</p>
+
+<div>{{EmbedInteractiveExample("pages/js/functions-definitions.html")}}</div>
+
+
+
+<h2 id="語法">語法</h2>
+
+<pre class="syntaxbox">var obj = {
+  <var>property</var>( <var>parameters…</var> ) {},
+  *<var>generator</var>( <var>parameters…</var> ) {},
+  async property( <var>parameters…</var> ) {},
+  async* generator( <var>parameters…</var> ) {},
+
+  // with computed keys:
+  [property]( <var>parameters…</var> ) {},
+  *[generator]( <var>parameters…</var> ) {},
+  async [property]( <var>parameters…</var> ) {},
+
+  // compare getter/setter syntax:
+  get <var>property</var>() {},
+  set <var>property</var>(<var>value</var>) {}
+};
+</pre>
+
+<h2 id="說明">說明</h2>
+
+<p>這個簡短的語法和在 ECMAScript 2015 引入 <a href="/en-US/docs/Web/JavaScript/Reference/Functions/get">getter</a> 以及 <a href="/en-US/docs/Web/JavaScript/Reference/Functions/set">setter</a> 類似。</p>
+
+<p>請看以下程式碼：</p>
+
+<pre class="brush: js">var obj = {
+  foo: function() {
+    /* code */
+  },
+  bar: function() {
+    /* code */
+  }
+};
+</pre>
+
+<p>你可以把它縮減為：</p>
+
+<pre class="brush: js">var obj = {
+  foo() {
+    /* code */
+  },
+  bar() {
+    /* code */
+  }
+};
+</pre>
+
+<h3 id="產生器方法">產生器方法</h3>
+
+<p><a href="/zh-TW/docs/Web/JavaScript/Reference/Statements/function*">產生器方法</a>（Generator method）也可以透過簡短語法定義之。用的時候：</p>
+
+<ul>
+ <li>簡短語法的星號（*）必須放在產生器方法的屬性名前面。也就是說 <code>* g(){}</code> 能動但 <code>g *(){}</code> 不行；</li>
+ <li>
+  <p>非產生器方法的定義可能不會有 <code>yield</code> 關鍵字。也就是說<a href="/zh-TW/docs/Web/JavaScript/Reference/Statements/Legacy_generator_function">過往的產生器函式</a>動不了、並拋出{{jsxref("SyntaxError")}}。Always use <code>yield</code> in conjunction with the asterisk (*).</p>
+ </li>
+</ul>
+
+<pre class="brush: js;highlight[12]">// Using a named property
+var obj2 = {
+  g: function* () {
+    var index = 0;
+    while (true)
+      yield index++;
+  }
+};
+
+// The same object using shorthand syntax
+var obj2 = {
+  * g() {
+    var index = 0;
+    while (true)
+      yield index++;
+  }
+};
+
+var it = obj2.g();
+console.log(it.next().value); // 0
+console.log(it.next().value); // 1</pre>
+
+<h3 id="Async_方法">Async 方法</h3>
+
+<p>{{jsxref("Statements/async_function", "Async 方法", "", 1)}} 也可以透過簡短語法定義。</p>
+
+<pre class="brush: js;highlight[12]">// Using a named property
+var obj3 = {
+  f: async function () {
+    await some_promise;
+  }
+};
+
+// The same object using shorthand syntax
+var obj3 = {
+  async f() {
+    await some_promise;
+  }
+};
+</pre>
+
+<h3 id="Async_generator_methods">Async generator methods</h3>
+
+<p><a href="/en-US/docs/Web/JavaScript/Reference/Statements/function*">Generator methods</a> can also be {{jsxref("Statements/async_function", "async", "", 1)}}.</p>
+
+<pre class="brush: js">var obj4 = {
+  f: async function* () {
+    yield 1;
+    yield 2;
+    yield 3;
+  }
+};
+
+// The same object using shorthand syntax
+var obj4 = {
+  async* f() {
+   yield 1;
+   yield 2;
+   yield 3;
+  }
+};</pre>
+
+<h3 id="Method_definitions_are_not_constructable">Method definitions are not constructable</h3>
+
+<p>All method definitions are not constructors and will throw a {{jsxref("TypeError")}} if you try to instantiate them.</p>
+
+<pre class="brush: js example-bad">var obj = {
+  method() {}
+};
+new obj.method; // TypeError: obj.method is not a constructor
+
+var obj = {
+  * g() {}
+};
+new obj.g; // TypeError: obj.g is not a constructor (changed in ES2016)
+</pre>
+
+<h2 id="範例">範例</h2>
+
+<h3 id="Simple_test_case">Simple test case</h3>
+
+<pre class="brush: js;highlight[3]">var obj = {
+  a: 'foo',
+  b() { return this.a; }
+};
+console.log(obj.b()); // "foo"
+</pre>
+
+<h3 id="Computed_property_names">Computed property names</h3>
+
+<p>The shorthand syntax also supports computed property names.</p>
+
+<pre class="brush: js;highlight[4]">var bar = {
+  foo0: function() { return 0; },
+  foo1() { return 1; },
+  ['foo' + 2]() { return 2; }
+};
+
+console.log(bar.foo0()); // 0
+console.log(bar.foo1()); // 1
+console.log(bar.foo2()); // 2</pre>
+
+<h2 id="規範">規範</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('ES2015', '#sec-method-definitions', 'Method definitions')}}</td>
+   <td>{{Spec2('ES2015')}}</td>
+   <td>Initial definition.</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ES2016', '#sec-method-definitions', 'Method definitions')}}</td>
+   <td>{{Spec2('ES2016')}}</td>
+   <td>Changed that generator methods should also not have a [[Construct]] trap and will throw when used with <code>new</code>.</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#sec-method-definitions', 'Method definitions')}}</td>
+   <td>{{Spec2('ESDraft')}}</td>
+   <td> </td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="瀏覽器相容性">瀏覽器相容性</h2>
+
+
+
+<p>{{Compat("javascript.functions.method_definitions")}}</p>
+
+<h2 id="參見">參見</h2>
+
+<ul>
+ <li><code><a href="/zh-TW/docs/Web/JavaScript/Reference/Functions/get">get</a></code></li>
+ <li><code><a href="/zh-TW/docs/Web/JavaScript/Reference/Functions/set">set</a></code></li>
+ <li><a href="/zh-TW/docs/Web/JavaScript/Reference/Lexical_grammar">Lexical grammar</a></li>
+</ul>