mirror of
https://github.com/fofolee/uTools-Manuals.git
synced 2025-06-08 23:14:06 +08:00
253 lines
16 KiB
HTML
253 lines
16 KiB
HTML
<article id="wikiArticle">
|
||
<div></div>
|
||
<p><code><strong>Array.from()</strong></code> 方法从一个类似数组或可迭代对象中创建一个新的数组实例。</p>
|
||
<div><iframe class="interactive interactive-js" frameborder="0" height="250" src="https://interactive-examples.mdn.mozilla.net/pages/js/array-from.html" width="100%"></iframe></div>
|
||
<p class="hidden">The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone <a class="external" href="https://github.com/mdn/interactive-examples" rel="noopener">https://github.com/mdn/interactive-examples</a> and send us a pull request.</p>
|
||
<h2 id="Syntax" name="Syntax">语法</h2>
|
||
<pre><code class="language-javascript"><code>Array.from(arrayLike[, mapFn[, thisArg]])
|
||
</code></code></pre>
|
||
<h3 id="Parameters" name="Parameters">参数</h3>
|
||
<dl>
|
||
<dt><code>arrayLike</code></dt>
|
||
<dd>想要转换成数组的伪数组对象或可迭代对象。</dd>
|
||
<dt><code>mapFn (可选参数) </code></dt>
|
||
<dd>如果指定了该参数，新数组中的每个元素会执行该回调函数。</dd>
|
||
<dt><code>thisArg (可选参数)</code></dt>
|
||
<dd>可选参数，执行回调函数 <code>mapFn</code> 时 <code>this</code> 对象。</dd>
|
||
</dl>
|
||
<h3 id="返回值">返回值</h3>
|
||
<p>一个新的数组实例</p>
|
||
<h2 id="描述">描述</h2>
|
||
<p><code>Array.from()</code> 可以通过以下方式来创建数组对象：</p>
|
||
<ul>
|
||
<li>伪数组对象（拥有一个 <code>length</code> 属性和若干索引属性的任意对象）</li>
|
||
<li><a href="Guide/iterable">可迭代对象</a>（可以获取对象中的元素,如 Map和 Set 等）</li>
|
||
</ul>
|
||
<p><code>Array.from()</code> 方法有一个可选参数 <code>mapFn</code>，让你可以在最后生成的数组上再执行一次 <a href="Reference/Global_Objects/Array/map" title="map() 方法创建一个新数组，其结果是该数组中的每个元素都调用一个提供的函数后返回的结果。"><code>map</code></a> 方法后再返回。也就是说<code> Array.from(obj, mapFn, thisArg) </code>就相当于<code> Array.from(obj).map(mapFn, thisArg),</code> 除非创建的不是可用的中间数组。 这对一些数组的子类<code>,</code>如 <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays">typed arrays</a><font face="Consolas, Liberation Mono, Courier, monospace"> 来说很重要,</font> 因为中间数组的值在调用 map() 时需要是适当的类型。</p>
|
||
<p><code>from()</code> 的 <code>length</code> 属性为 1 ，即<code>Array.from.length = 1</code>。</p>
|
||
<p>在 ES2015 中， <code>Class</code> 语法允许我们为内置类型（比如 <code>Array</code>）和自定义类新建子类（比如叫 <code>SubArray</code>）。这些子类也会继承父类的静态方法，比如 <code>SubArray.from()</code>，调用该方法后会返回子类 <code>SubArray</code> 的一个实例，而不是 <code>Array</code> 的实例。</p>
|
||
<h2 id="示例">示例</h2>
|
||
<h3 id="Array_from_a_String">Array from a <code>String</code></h3>
|
||
<pre><code class="language-javascript">Array.from('foo');
|
||
// ["f", "o", "o"]</code></pre>
|
||
<h3 id="Array_from_a_Set">Array from a <code>Set</code></h3>
|
||
<pre><code class="language-javascript">let s = new Set(['foo', window]);
|
||
Array.from(s);
|
||
// ["foo", window]
|
||
</code></pre>
|
||
<h3 id="Array_from_a_Map">Array from a <code>Map</code></h3>
|
||
<pre><code class="language-javascript">let m = new Map([[1, 2], [2, 4], [4, 8]]);
|
||
Array.from(m);
|
||
// [[1, 2], [2, 4], [4, 8]]
|
||
</code></pre>
|
||
<h3 id="Array_from_an_Array-like_object_(arguments)">Array from an Array-like object (arguments)</h3>
|
||
<pre><code class="language-javascript">function f() {
|
||
return Array.from(arguments);
|
||
}
|
||
|
||
f(1, 2, 3);
|
||
|
||
// [1, 2, 3]</code></pre>
|
||
<h3 id="在Array.from中使用箭头函数">在<code>Array.from</code>中使用箭头函数</h3>
|
||
<pre><code class="language-javascript">// Using an arrow function as the map function to
|
||
// manipulate the elements
|
||
Array.from([1, 2, 3], x => x + x);
|
||
// x => x + x代表这是一个函数，只是省略了其他的定义，这是一种Lambda表达式的写法
|
||
// 箭头的意思表示从当前数组中取出一个值，然后自加，并将返回的结果添加到新数组中
|
||
// [2, 4, 6]
|
||
|
||
|
||
// Generate a sequence of numbers
|
||
// Since the array is initialized with `undefined` on each position,
|
||
// the value of `v` below will be `undefined`
|
||
Array.from({length: 5}, (v, i) => i);
|
||
// [0, 1, 2, 3, 4]
|
||
</code></pre>
|
||
<h3 id="数组去重合并">数组去重合并</h3>
|
||
<pre><code class="language-javascript">function combine(){
|
||
let arr = [].concat.apply([], arguments); //没有去重复的新数组
|
||
return Array.from(new Set(arr));
|
||
}
|
||
|
||
var m = [1, 2, 2], n = [2,3,3];
|
||
console.log(combine(m,n)); // [1, 2, 3]</code></pre>
|
||
<h2 id="Polyfill">Polyfill</h2>
|
||
<p>ECMA-262 第六版标准添加了<code> Array.from </code>。有些实现中可能尚未包括在其中。你可以通过在脚本前添加如下内容作为替代方法，以使用未原生支持的 <code>Array.from</code> 方法。该算法按照 ECMA-262 第六版中的规范实现，并假定 <code>Object</code> 和 <code>TypeError</code> 有其本身的值， <code>callback.call</code> 对应 <a href="Reference/Global_Objects/Function/call" title="call() 方法调用一个函数, 其具有一个指定的this值和分别地提供的参数(参数的列表)。"><code>Function.prototype.call</code></a> 。此外，鉴于无法使用 Polyfill 实现真正的的迭代器，该实现不支持规范中定义的泛型可迭代元素。</p>
|
||
<pre><code class="language-javascript">// Production steps of ECMA-262, Edition 6, 22.1.2.1
|
||
// Reference: https://people.mozilla.org/~jorendorff/es6-draft.html#sec-array.from
|
||
if (!Array.from) {
|
||
Array.from = (function () {
|
||
var toStr = Object.prototype.toString;
|
||
var isCallable = function (fn) {
|
||
return typeof fn === 'function' || toStr.call(fn) === '[object Function]';
|
||
};
|
||
var toInteger = function (value) {
|
||
var number = Number(value);
|
||
if (isNaN(number)) { return 0; }
|
||
if (number === 0 || !isFinite(number)) { return number; }
|
||
return (number > 0 ? 1 : -1) * Math.floor(Math.abs(number));
|
||
};
|
||
var maxSafeInteger = Math.pow(2, 53) - 1;
|
||
var toLength = function (value) {
|
||
var len = toInteger(value);
|
||
return Math.min(Math.max(len, 0), maxSafeInteger);
|
||
};
|
||
var toItems = function (value) {
|
||
// support set
|
||
if (value.size > 0 && value.values) {
|
||
let values = value.values()
|
||
var it = values.next()
|
||
var o = []
|
||
while (!it.done) {
|
||
o.push(it.value)
|
||
it = values.next()
|
||
}
|
||
return o
|
||
}
|
||
return Object(value);
|
||
};
|
||
// The length property of the from method is 1.
|
||
return function from(arrayLike/*, mapFn, thisArg */) {
|
||
// 1. Let C be the this value.
|
||
var C = this;
|
||
|
||
// 2. Let items be ToObject(arrayLike).
|
||
var items = toItems(arrayLike);
|
||
|
||
// 3. ReturnIfAbrupt(items).
|
||
if (arrayLike == null) {
|
||
throw new TypeError("Array.from requires an array-like object - not null or undefined");
|
||
}
|
||
|
||
// 4. If mapfn is undefined, then let mapping be false.
|
||
var mapFn = arguments.length > 1 ? arguments[1] : void undefined;
|
||
var T;
|
||
if (typeof mapFn !== 'undefined') {
|
||
// 5. else
|
||
// 5. a If IsCallable(mapfn) is false, throw a TypeError exception.
|
||
if (!isCallable(mapFn)) {
|
||
throw new TypeError('Array.from: when provided, the second argument must be a function');
|
||
}
|
||
|
||
// 5. b. If thisArg was supplied, let T be thisArg; else let T be undefined.
|
||
if (arguments.length > 2) {
|
||
T = arguments[2];
|
||
}
|
||
}
|
||
|
||
// 10. Let lenValue be Get(items, "length").
|
||
// 11. Let len be ToLength(lenValue).
|
||
var len = toLength(items.length);
|
||
|
||
// 13. If IsConstructor(C) is true, then
|
||
// 13. a. Let A be the result of calling the [[Construct]] internal method
|
||
// of C with an argument list containing the single item len.
|
||
// 14. a. Else, Let A be ArrayCreate(len).
|
||
var A = isCallable(C) ? Object(new C(len)) : new Array(len);
|
||
|
||
// 16. Let k be 0.
|
||
var k = 0;
|
||
// 17. Repeat, while k < len… (also steps a - h)
|
||
var kValue;
|
||
while (k < len) {
|
||
kValue = items[k];
|
||
if (mapFn) {
|
||
A[k] = typeof T === 'undefined' ? mapFn(kValue, k) : mapFn.call(T, kValue, k);
|
||
} else {
|
||
A[k] = kValue;
|
||
}
|
||
k += 1;
|
||
}
|
||
// 18. Let putStatus be Put(A, "length", len, true).
|
||
A.length = len;
|
||
// 20. Return A.
|
||
return A;
|
||
};
|
||
}());
|
||
}
|
||
</code></pre>
|
||
<h2 id="规范">规范</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><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-array.from" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Array.from</small></a></td>
|
||
<td><span class="spec-Standard">Standard</span></td>
|
||
<td>Initial definition.</td>
|
||
</tr>
|
||
<tr>
|
||
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-array.from" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Array.from</small></a></td>
|
||
<td><span class="spec-Draft">Draft</span></td>
|
||
<td> </td>
|
||
</tr>
|
||
</tbody>
|
||
</table>
|
||
<h2 id="浏览器兼容性">浏览器兼容性</h2>
|
||
<div>
|
||
<div class="hidden">The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out <a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</div>
|
||
<p></p><div class="bc-data"><a class="bc-github-link external" href="https://github.com/mdn/browser-compat-data" rel="noopener">Update compatibility data on GitHub</a><table class="bc-table bc-table-js"><thead><tr class="bc-platforms"><td></td><th class="bc-platform-desktop" colspan="6"><span>Desktop</span></th><th class="bc-platform-mobile" colspan="7"><span>Mobile</span></th><th class="bc-platform-server" colspan="1"><span>Server</span></th></tr><tr class="bc-browsers"><td></td><th class="bc-browser-chrome"><span class="bc-head-txt-label bc-head-icon-chrome">Chrome</span></th><th class="bc-browser-edge"><span class="bc-head-txt-label bc-head-icon-edge">Edge</span></th><th class="bc-browser-firefox"><span class="bc-head-txt-label bc-head-icon-firefox">Firefox</span></th><th class="bc-browser-ie"><span class="bc-head-txt-label bc-head-icon-ie">Internet Explorer</span></th><th class="bc-browser-opera"><span class="bc-head-txt-label bc-head-icon-opera">Opera</span></th><th class="bc-browser-safari"><span class="bc-head-txt-label bc-head-icon-safari">Safari</span></th><th class="bc-browser-webview_android"><span class="bc-head-txt-label bc-head-icon-webview_android">Android webview</span></th><th class="bc-browser-chrome_android"><span class="bc-head-txt-label bc-head-icon-chrome_android">Chrome for Android</span></th><th class="bc-browser-edge_mobile"><span class="bc-head-txt-label bc-head-icon-edge_mobile">Edge Mobile</span></th><th class="bc-browser-firefox_android"><span class="bc-head-txt-label bc-head-icon-firefox_android">Firefox for Android</span></th><th class="bc-browser-opera_android"><span class="bc-head-txt-label bc-head-icon-opera_android">Opera for Android</span></th><th class="bc-browser-safari_ios"><span class="bc-head-txt-label bc-head-icon-safari_ios">Safari on iOS</span></th><th class="bc-browser-samsunginternet_android"><span class="bc-head-txt-label bc-head-icon-samsunginternet_android">Samsung Internet</span></th><th class="bc-browser-nodejs"><span class="bc-head-txt-label bc-head-icon-nodejs">Node.js</span></th></tr></thead><tbody><tr><th scope="row"><code>from</code></th><td class="bc-supports-yes bc-browser-chrome"><span class="bc-browser-name">Chrome</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
45</td><td class="bc-supports-yes bc-browser-edge"><span class="bc-browser-name">Edge</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
12</td><td class="bc-supports-yes bc-browser-firefox"><span class="bc-browser-name">Firefox</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
32</td><td class="bc-supports-no bc-browser-ie"><span class="bc-browser-name">IE</span><abbr class="bc-level-no only-icon" title="No support">
|
||
<span>No support</span>
|
||
</abbr>
|
||
No</td><td class="bc-supports-yes bc-browser-opera"><span class="bc-browser-name">Opera</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
Yes</td><td class="bc-supports-yes bc-browser-safari"><span class="bc-browser-name">Safari</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
9</td><td class="bc-supports-unknown bc-browser-webview_android"><span class="bc-browser-name">WebView Android</span><abbr title="Compatibility unknown; please update this.">
|
||
?
|
||
</abbr></td><td class="bc-supports-yes bc-browser-chrome_android"><span class="bc-browser-name">Chrome Android</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
Yes</td><td class="bc-supports-yes bc-browser-edge_mobile"><span class="bc-browser-name">Edge Mobile</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
Yes</td><td class="bc-supports-yes bc-browser-firefox_android"><span class="bc-browser-name">Firefox Android</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
32</td><td class="bc-supports-yes bc-browser-opera_android"><span class="bc-browser-name">Opera Android</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
Yes</td><td class="bc-supports-yes bc-browser-safari_ios"><span class="bc-browser-name">Safari iOS</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
Yes</td><td class="bc-supports-yes bc-browser-samsunginternet_android"><span class="bc-browser-name">Samsung Internet Android</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
Yes</td><td class="bc-supports-yes bc-browser-nodejs"><span class="bc-browser-name">nodejs</span><abbr class="bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
</abbr>
|
||
4.0.0</td></tr></tbody></table><section class="bc-legend" id="sect1"><h3 class="offscreen" id="Legend">Legend</h3><dl><dt><span class="bc-supports-yes bc-supports">
|
||
<abbr class="bc-level bc-level-yes only-icon" title="Full support">
|
||
<span>Full support</span>
|
||
|
||
</abbr></span></dt><dd>Full support</dd><dt><span class="bc-supports-no bc-supports">
|
||
<abbr class="bc-level bc-level-no only-icon" title="No support">
|
||
<span>No support</span>
|
||
|
||
</abbr></span></dt><dd>No support</dd><dt><span class="bc-supports-unknown bc-supports">
|
||
<abbr class="bc-level bc-level-unknown only-icon" title="Compatibility unknown">
|
||
<span>Compatibility unknown</span>
|
||
|
||
</abbr></span></dt><dd>Compatibility unknown</dd></dl></section></div><p></p>
|
||
</div>
|
||
<h2 id="相关链接">相关链接</h2>
|
||
<ul>
|
||
<li><a href="Reference/Array" title="REDIRECT Array"><code>Array</code></a></li>
|
||
<li><a href="Reference/Global_Objects/Array/map" title="map() 方法创建一个新数组，其结果是该数组中的每个元素都调用一个提供的函数后返回的结果。"><code>Array.prototype.map()</code></a></li>
|
||
<li><a href="Reference/Global_Objects/TypedArray/from" title="TypedArray.from() 方法 从一个类数组或者可迭代对象中创建一个新类型数组。 这个方法和 Array.from()类似。"><code>TypedArray.from()</code></a></li>
|
||
</ul>
|
||
</article> |