ES10

JSON.stringify() 修复bug

console.log(JSON.stringify('\u{D800}'))//ES10之前会报错

arr.flat(depth)

以递归方式按指定深度进行扁平化输出

let arr = [1,[2,3],[4,5,[6,7,[8,9,10]]]]
console.log(arr.flat()) //(6) [1, 2, 3, 4, 5, Array(3)],没传参数的时候：默认值是1
console.log(arr.flat(10))//(10) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

let arr1 = [1,2,3]
console.log(arr1.flatMap(item=>[item*2])) //(3) [2, 4, 6]

[字符串] trimStart trimLeft trimEnd trimRight

let str = '  foo  '
console.log(str.trimStart()) //foo  trimStart和trimLeft一样
console.log(str.trimEnd())//  foo,trimEnd和trimRight一样
console.log(str.trim())//foo,去除首尾空格