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ES6 spread操作符、rest操作符、Destructuring解构赋值 - 读书笔记
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<h1>ES6 spread操作符、rest操作符、Destructuring解构赋值</h1>
<div class="read-more clearfix">
<span class="date">2018/1/28</span>
<span>posted in </span>
<span class="posted-in"><a href='ECMA6.html'>ECMA6</a></span>
<span class="comments">
</span>
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<h4 id="toc_0">rest 参数(函数里使用)</h4>
<p>ES6 引入 rest 参数（形式为...变量名），用于获取函数的多余参数，这样就不需要使用arguments对象了。rest 参数搭配的变量是一个数组，该变量将多余的参数放入数组中。</p>
<p>函数里用 参数用…reset 是把参数数字转成数组</p>
<pre><code>function add(...values) {
let sum = 0;
for (var val of values) {
sum += val;
}
return sum;
}
add(2, 5, 3) // 10
// arguments变量的写法
function sortNumbers() {
return Array.prototype.slice.call(arguments).sort();
}
// rest参数的写法
const sortNumbers = (...numbers) => numbers.sort();
</code></pre>
<span id="more"></span><!-- more -->
<h4 id="toc_1">扩展运算符（数组里使用）</h4>
<p>扩展运算符（spread）是三个点（...）。它好比 rest 参数的逆运算，将一个数组转为用逗号分隔的参数序列。<br/>
… spread 是扩展运算符，目地是把数组解构成用逗号分隔的参数序列</p>
<pre><code>console.log(...[1, 2, 3])
// 1 2 3
console.log(1, ...[2, 3, 4], 5)
// 1 2 3 4 5
[...document.querySelectorAll('div')]
// [<div>, <div>, <div>]
function push(array, ...items) {
// 反转成数组
array.push(...items);
}
function add(x, y) {
return x + y;
}
const numbers = [4, 38];
// 解构成字符
add(...numbers) // 42
</code></pre>
<p>上面代码中，array.push(...items)和add(...numbers)这两行，都是函数的调用，它们的都使用了扩展运算符。该运算符将一个数组，变为参数序列。</p>
<h4 id="toc_2">替代函数的 apply 方法</h4>
<pre><code>// ES5 的写法
function f(x, y, z) {
// ...
}
var args = [0, 1, 2];
f.apply(null, args);
// ES6的写法
function f(x, y, z) {
// ...
}
let args = [0, 1, 2];
f(...args);
// ES5 的写法
Math.max.apply(null, [14, 3, 77])
// ES6 的写法
Math.max(...[14, 3, 77])
// 等同于
Math.max(14, 3, 77);
</code></pre>
<p>当…作为函数实参或=号右侧时用作spread运算符<br/>
当…作为函数形参或=号左侧时用作rest操作符</p>
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