Object.fromEntries
Object.fromEntries用来创建对象,但是它的参数比较特殊,是二维数组或一个map
eg:
// 二维数组
const result1 = Object.fromEntries([
['name','yang'],
['age','19'],
])
console.log(result1)
// map
const m =new Map()
m.set('name','yang')
const result2 = Object.fromEntries(m)
console.log(result2)
- Object.fromEntries将二维数组转换成对象
- Object.Entries将对象转换成二维数组
字符串扩展
trimStart与trimEnd
trimStart清除字符串左侧空白
trimEnd 清除字符串右侧空白
let = str =" helloWorld "
console.log(str)
console.log(str.trimStart())
console.log(str.trimEnd())
数组方法扩展
flat
flat()
:将多维数组转化为低维数组
flat可以有参数: flat(n),n表示将维的深度,如三维=>一维,n=2。默认情况下n=1
eg:二维=>一维
const arr =[1,2,3,4,[5,6]]
console.log(arr.flat())
三维=>二维
const arr =[1,2,3,4,[5,6,[7,8,9]]]
console.log(arr.flat())
三维=>一维
const arr =[1,2,3,4,[5,6,[7,8,9]]]
console.log(arr.flat(2))
flatMap
将map的返回结果变成一维的
eg:
const arr =[1,2,3,4]
const result = arr.map(item=>[item*10])
console.log(result)
const result2 = arr.flatMap(item=>[item*10])
console.log(result2)
Symbol
Symbol.prototype.description获取symbol属性值。
eg:
let s =Symbol('yang')
console.log(s.description)
输出: