TypedArray.from(source[, mapFn[, thisArg]])
					

• Int8Array
• Uint8Array
• Uint8ClampedArray
• Int16Array
• Uint16Array
• Int32Array
• Uint32Array
• Float32Array
• Float64Array
• BigInt64Array
• BigUint64Array

参数

source

An array-like or iterable object to convert to a typed array.

mapFn 可选

Map function to call on every element of the typed array.

thisArg 可选

Value to use as this when executing mapFn .

返回值

A new TypedArray 实例。

描述

TypedArray .from() lets you create typed arrays from:

• array-like objects (objects with a length property and indexed elements); or
• iterable objects (objects where you can get its elements, such as Map and Set ).

TypedArray .from() has the optional parameter mapFn , which allows you to execute a map() function on each element of the typed array (or subclass object) that is being created. This means that the following are equivalent:

• TypedArray .from( obj , mapFn , thisArg )
• TypedArray .from(Array.prototype.map.call( obj , mapFn , thisArg )) .

length 特性为 from() method is 1 .

Differences from Array.from()

Some subtle distinctions between Array.from() and TypedArray .from() :

• 若 thisArg value passed to TypedArray.from() is not a constructor, TypedArray.from() will throw a TypeError , where Array.from() defaults to creating a new Array .
• TypedArray.from() 使用 [[Put]] where Array.from() 使用 [[DefineProperty]] . Hence, when working with Proxy objects, it calls handler.set to create new elements rather than handler.defineProperty() .
• When the source parameter is an iterator, the TypedArray.from() first collects all the values from the iterator, then creates an instance of thisArg using the count, then sets the values on the instance. Array.from() sets each value as it receives them from the iterator, then sets its length at the end.
• When Array.from() gets an array-like which isn't an iterator, it respects holes. TypedArray.from() will ensure the result is dense.

Polyfill

You can partially work around this by inserting the following code at the beginning of your scripts, allowing use of much of the functionality of from() in implementations that do not natively support it.

if (!Int8Array.__proto__.from) {
    (function () {
        Int8Array.__proto__.from = function (obj, func, thisObj) {
            var typedArrayClass = Int8Array.__proto__;
            if(typeof this !== 'function') {
                throw new TypeError('# is not a constructor');
            }
            if (this.__proto__ !== typedArrayClass) {
                throw new TypeError('this is not a typed array.');
            }
            func = func || function (elem) {
                    return elem;
                };
            if (typeof func !== 'function') {
                throw new TypeError('specified argument is not a function');
            }
            obj = Object(obj);
            if (!obj['length']) {
                return new this(0);
            }
            var copy_data = [];
            for(var i = 0; i < obj.length; i++) {
                copy_data.push(obj[i]);
            }
            copy_data = copy_data.map(func, thisObj);
            var typed_array = new this(copy_data.length);
            for(var i = 0; i < typed_array.length; i++) {
                typed_array[i] = copy_data[i];
            }
            return typed_array;
        }
    })();
}
							

范例

From an iterable object (Set)

const s = new Set([1, 2, 3]);
Uint8Array.from(s);
// Uint8Array [ 1, 2, 3 ]
							

From a string

Int16Array.from('123');
// Int16Array [ 1, 2, 3 ]
							

Use with arrow function and map

Using an arrow function as the map function to manipulate the elements

Float32Array.from([1, 2, 3], x => x + x);
// Float32Array [ 2, 4, 6 ]
							

Generate a sequence of numbers

Uint8Array.from({length: 5}, (v, k) => k);
// Uint8Array [ 0, 1, 2, 3, 4 ]
							

规范

规范
ECMAScript (ECMA-262) The definition of '%TypedArray%.from' in that specification.

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
from	Chrome 45	Edge 14	Firefox 38	IE No	Opera No	Safari 10	WebView Android No	Chrome Android No	Firefox Android 38	Opera Android No	Safari iOS 10	Samsung Internet Android No	nodejs 4.0.0

图例

完整支持

完整支持

不支持

不支持

另请参阅

• TypedArray.of()
• Array.from()
• Array.prototype.map()

元数据

• 最后修改： Aug 7, 2020