ES6 语法记录(迭代)

本文主要记录在使用Vue开发前端页面时,遇到的前端ES知识点整理.

 

1:  ...(三个点) 运算符

  合并数组,   

 合并数组时与ES5的 concat方法一致

var list=[1,2,23,4]
undefined
var a=list[0]
undefined
a
1
rest=list.slice(1)
(3) [2, 23, 4]
[a,...rest]
(4) [1, 2, 23, 4]

当合并obj对象时,将对象作为数组0,继续组合...b的数组

var a={}
undefined
b
(4) [1, 2, 3, 4]
[a,...b]
(5) [{…}, 1, 2, 3, 4]
0: {}
1: 1
2: 2
3: 3
4: 4
length: 5
__proto__: Array(0)

...如果用于数组赋值,则必须放到最后

如以下会报错

如果将扩展运算符用于数组赋值，只能放在参数的最后一位，否则会报错

const [...butLast, last] = [1, 2, 3, 4, 5];

const [first, ...middle, last] = [1, 2, 3, 4, 5];

用于字符串时,表示将字符串拆分

[...'helloword']
(9) ["h", "e", "l", "l", "o", "w", "o", "r", "d"]
0: "h"
1: "e"
2: "l"
3: "l"
4: "o"
5: "w"
6: "o"
7: "r"
8: "d"
length: 9
__proto__: Array(0)

用于Map

let map=new Map([[1,'one','two']]);
undefined
map
Map(1) {1 => "one"}
map[0]
undefined
map.1
VM1641:1 Uncaught SyntaxError: Unexpected number
map
Map(1) {1 => "one"}[[Entries]]0: {1 => "one"}size: (...)__proto__: Map
map.keys()
MapIterator {1}[[Entries]]0: 1__proto__: Map Iterator[[IteratorHasMore]]: true[[IteratorIndex]]: 0[[IteratorKind]]: "keys"
[...nap.keys()]
VM1757:1 Uncaught ReferenceError: nap is not defined
    at <anonymous>:1:1
(anonymous) @ VM1757:1
[...map.keys()]
[1]