Array.from()
可以通过以下方式来创建数组对象:
- 伪数组对象(拥有一个
length
属性和若干索引属性的任意对象) - 可迭代对象(可以获取对象中的元素,如 Map和 Set 等)
Array.from()
方法有一个可选参数 mapFn
,让你可以在最后生成的数组上再执行一次 map
方法后再返回。也就是说 Array.from(obj, mapFn, thisArg)
就相当于 Array.from(obj).map(mapFn, thisArg);
示例 Array from a String Array.from(‘foo‘); // ["f", "o", "o"] Array from a Set let s = new Set([‘foo‘, window]); Array.from(s); // ["foo", window] Array from a Map let m = new Map([[1, 2], [2, 4], [4, 8]]); Array.from(m); // [[1, 2], [2, 4], [4, 8]] Array from an Array-like object (arguments) function f() { return Array.from(arguments); } f(1, 2, 3); // [1, 2, 3] Using arrow functions and Array.from // Using an arrow function as the map function to // manipulate the elements Array.from([1, 2, 3], x => x + x); // [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]