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---
title: 'TypeError: ''x'' is not iterable'
slug: Web/JavaScript/Reference/Errors/is_not_iterable
tags:
- 生成器
- 迭代器
translation_of: Web/JavaScript/Reference/Errors/is_not_iterable
---
<div>{{jsSidebar("Errors")}}</div>
<h2 id="错误信息">错误信息</h2>
<pre class="syntaxbox">TypeError: 'x' is not iterable (Firefox, Chrome)
TypeError: 'x' is not a function or its return value is not iterable (Chrome)
</pre>
<h2 id="错误类型">错误类型</h2>
<p>{{jsxref("TypeError")}}</p>
<h2 id="发生了什么错误">发生了什么错误?</h2>
<p>这个值作为 <a href="/en-US/docs/Web/JavaScript/Guide/Loops_and_iteration#for...of_statement">for…of </a>的表达式右值，或者作为一个函数的参数，如 {{jsxref("Promise.all")}} 或者 {{jsxref("TypedArray.from")}}, 不是一个 <a href="/en-US/docs/Web/JavaScript/Reference/Iteration_protocols">可迭代对象</a>. 一个可迭代对象可以是一个内置可迭代类型，如{{jsxref("Array")}}, {{jsxref("String")}} 或 {{jsxref("Map")}}, 一个 generator 生成结果, 或者一个实现了 <a href="/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol">可迭代协议</a> 的对象</p>
<h2 id="示例">示例</h2>
<h3 id="Iterating_over_Object_properties">Iterating over Object properties</h3>
<p>在JavaScript中, {{jsxref("Object")}} 是不可迭代的，除非它们实现了<a href="/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol">迭代协议</a>. 因此, 你不能使用 <a href="/en-US/docs/Web/JavaScript/Guide/Loops_and_iteration#for...of_statement">for…of </a>来迭代对象的属性.</p>
<pre class="brush: js example-bad">var obj = { 'France': 'Paris', 'England': 'London' };
for (let p of obj) { // TypeError: obj is not iterable
// …
}
</pre>
<p>做为替代你必须使用 {{jsxref("Object.keys")}} 或 {{jsxref("Object.entries")}} 来迭代对象的属性或属性值.</p>
<pre class="brush: js example-good">var obj = { 'France': 'Paris', 'England': 'London' };
// 迭代属性名称:
for (let country of <code>Object</code>.keys(obj)) {
var capital = obj[country];
console.log(country, capital);
}
for (const [country, capital] of <code>Object</code>.entries(obj))
console.log(country, capital);
</pre>
<p>这次case的另外一个选择是使用 {{jsxref("Map")}}:</p>
<pre class="brush: js example-good">var map = new Map;
map.set('France', 'Paris');
map.set('England', 'London');
// Iterate over the property names:
for (let country of map.keys()) {
let capital = map[country];
console.log(country, capital);
}
for (let capital of map.values())
console.log(capital);
for (const [country, capital] of map.entries())
console.log(country, capital);
</pre>
<h3 id="Iterating_over_a_generator">Iterating over a generator</h3>
<p><a href="/en-US/docs/Web/JavaScript/Guide/Iterators_and_Generators#Generators">Generators</a> 是用来生成可迭代对象的函数.</p>
<pre class="brush: js example-bad">function* generate(a, b) {
yield a;
yield b;
}
for (let x of generate) // TypeError: generate is not iterable
console.log(x);
</pre>
<p>当它没有被调用, 这个 {{jsxref("Function")}} 相应的是可调用的，但是不可迭代。 调用 generator 生成一个可迭代对象，该对象将迭代在生成器执行期间生成的值.</p>
<pre class="brush: js example-good">function* generate(a, b) {
yield a;
yield b;
}
for (let x of generate(1,2))
console.log(x);</pre>
<h3 id="Iterating_over_a_custom_iterable">Iterating over a custom iterable</h3>
<p>可以使用{{jsxref("Symbol.iterator")}} 方法去实现一个自定义迭代器。你必须确定自定义的迭代器方法返回一个迭代器对象，即它必须有一个next()</p>
<pre class="brush: js example-bad">const myEmptyIterable = {
[Symbol.iterator]() {
return [] // [] is iterable, but it is not an iterator -- it has no next method.
}
}
Array.from(myEmptyIterable); // TypeError: myEmptyIterable is not iterable
</pre>
<pre></pre>
<p>下面是正确用法</p>
<pre class="brush: js example-good">const myEmptyIterable = {
[Symbol.iterator]() {
return [][Symbol.iterator]()
}
}
Array.from(myEmptyIterable); // []
</pre>
<h2 id="参阅">参阅</h2>
<ul>
<li><a href="/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol">iterable protocol</a></li>
<li>{{jsxref("Object.keys")}}</li>
<li>{{jsxref("Object.entries")}}</li>
<li>{{jsxref("Map")}}</li>
<li><a href="/en-US/docs/Web/JavaScript/Guide/Iterators_and_Generators#Generators">generators</a></li>
<li><a href="/en-US/docs/Web/JavaScript/Guide/Loops_and_iteration#for...of_statement">for…of</a></li>
</ul>
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