1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
|
---
title: handler.enumerate()
slug: Archive/Web/JavaScript/handler.enumerate
translation_of: Archive/Web/JavaScript/handler.enumerate
---
<div>{{JSRef}} {{obsolete_header}}</div>
<p>代理方法<strong><code>handler.enumerate()</code></strong>决定了被代理对象在{{jsxref("Statements/for...in", "for...in")}}中的行为。不过这个方法已经在ES2016标准中被移除了。</p>
<h2 id="语法">语法</h2>
<pre class="brush: js notranslate">var p = new Proxy(target, {
enumerate(target) {
}
});
</pre>
<h3 id="参数">参数</h3>
<p>下列参数将会被用以调用 <code>enumerate</code> 方法。this将会指向处理器对象。</p>
<dl>
<dt><code>target</code></dt>
<dd>被代理的目标对象。</dd>
</dl>
<h3 id="Return_value">Return value</h3>
<p>该方法应当返回一个<a href="/zh-CN/docs/Web/JavaScript/Guide/The_Iterator_protocol">迭代器</a>对象。</p>
<h2 id="描述">描述</h2>
<p><code><strong>handler.enumerate</strong></code> 方法决定了被代理对象在{{jsxref("Statements/for...in", "for...in")}}时的行为。</p>
<h3 id="触发条件">触发条件</h3>
<p>这些操作可以触发这个方法。</p>
<ul>
<li>for...in: <code>for (var name in proxy) {...}</code></li>
<li>{{jsxref("Reflect.enumerate()")}}</li>
</ul>
<h3 id="Invariants">Invariants</h3>
<p>If the following invariants are violated, the proxy will throw a {{jsxref("TypeError")}}:</p>
<ul>
<li>The <code>enumerate</code> method must return an object.</li>
</ul>
<h2 id="Examples">Examples</h2>
<p>The following code traps {{jsxref("Statements/for...in", "for...in")}} statements.</p>
<pre class="brush: js notranslate">var p = new Proxy({}, {
enumerate(target) {
console.log('called');
return ['a', 'b', 'c'][Symbol.iterator]();
}
});
for (var x in p) { // "called"
console.log(x); // "a"
} // "b"
// "c"
</pre>
<p>The following code violates the invariant.</p>
<pre class="brush: js notranslate">var p = new Proxy({}, {
enumerate(target) {
return 1;
}
});
for (var x in p) {} // TypeError is thrown
</pre>
<p>Note: Both examples make use of the shorthand syntax for <a href="/en-US/docs/Web/JavaScript/Reference/Functions/Method_definitions">method definitions</a>.</p>
<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('ES2015', '#sec-proxy-object-internal-methods-and-internal-slots-enumerate', '[[Enumerate]]')}}</td>
<td>{{Spec2('ES2015')}}</td>
<td>Initial definition. Removed in ECMAScript 2016.</td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<div>
<p>{{Compat("javascript.builtins.Proxy.handler.enumerate")}}</p>
</div>
<h2 id="See_also">See also</h2>
<ul>
<li>{{jsxref("Proxy")}}</li>
<li>{{jsxref("Proxy.handler", "handler")}}</li>
<li>{{jsxref("Statements/for...in", "for...in")}} statements</li>
<li>{{jsxref("Reflect.enumerate()")}}</li>
</ul>
|
