es6数组新增函数from()和of()

es6数组新增函数from()和of()

from()将可迭代结构转换为数组

console.log(Array.from('js')) // [ 'j', 's' ]

数组的浅复制

let a1 = ['js', 'html', 'css', {k1: 1, k2: 2}]
let a2 = Array.from(a1)
console.log(a2); // [ 'js', 'html', 'css', { k1: 1, k2: 2 } ]
console.log(a1[3] === a2[3]); // true

转换map

let m = new Map()
m.set('k1', '1')
m.set('k2', '2')
m.set('k3', '3')
m.set('k4', '4')
console.log(Array.from(m)); // [ [ 'k1', '1' ], [ 'k2', '2' ], [ 'k3', '3' ], [ 'k4', '4' ] ]
console.log(Array.from(m.values(), v => 'v' + v)); // [ 'v1', 'v2', 'v3', 'v4' ]

转换生成器

console.log(Array.from({
  * [Symbol.iterator]() {
    yield 1
    yield 2
  }
})) // [ 1, 2 ]

of()将所有参数转换为数组

console.log(Array.of('4', '3')) // [ '4', '3' ]
console.log(Array.of(undefined, null)) // [ undefined, null ]