ES6之Array.from()方法

1. 将类数组对象转换为真正数组：

let arrayLike = {
    0: 'tom', 
    1: '65',
    2: '男',
    3: ['jane','john','Mary'],
    'length': 4
}
let arr = Array.from(arrayLike)
console.log(arr) // ['tom','65','男',['jane','john','Mary']]

2.字符串转换成数组

Array.from('foo');
// [ "f", "o", "o" ]

3.从set生成数组

const set = new Set(['foo', 'bar', 'baz', 'foo']);
Array.from(set);
// [ "foo", "bar", "baz" ]

4.从Map生成数组

const map = new Map([[1, 2], [2, 4], [4, 8]]);
Array.from(map);
// [[1, 2], [2, 4], [4, 8]]

const mapper = new Map([['1', 'a'], ['2', 'b']]);
Array.from(mapper.values());
// ['a', 'b'];

Array.from(mapper.keys());
// ['1', '2'];

5.从类数组对象（arguments）生成数组

function f() {
  return Array.from(arguments);
}

f(1, 2, 3);

// [ 1, 2, 3 ]

6.在array.from中使用箭头函数

// 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]

7.序列生成器指定范围

// Sequence generator function (commonly referred to as "range", e.g. Clojure, PHP etc)
const range = (start, stop, step) => Array.from({ length: (stop - start) / step + 1}, (_, i) => start + (i * step));

// Generate numbers range 0..4
range(0, 4, 1);
// [0, 1, 2, 3, 4]

// Generate numbers range 1..10 with step of 2
range(1, 10, 2);
// [1, 3, 5, 7, 9]

// Generate the alphabet using Array.from making use of it being ordered as a sequence
range('A'.charCodeAt(0), 'Z'.charCodeAt(0), 1).map(x => String.fromCharCode(x));
// ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]

8.数组去重合并

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]