对象的函数解构
直接把这个JSON格式数据当作参数，传递到函数内部进行处理
let json = {
a:'jie',
b:'杰'
}
function fun({a,b}){
console.log(a,b);
}
fun(json) //jie 杰数组的函数解构
let arr =['jie','biao','nine'];
function fun(a,b,c){
console.log(a,b,c)
}
fun(...arr) //jie biao ninein
in是用来判断对象或者数组中是否存在某个值的
对象
let obj={
a:'jie'
}
console.log('a' in obj) // true
console.log('b' in obj) //false数组
这里的0指的是数组下标位置是否为空。
let arr = [,,,];
console.log(0 in arr); //false
let arr2 = ['jie','bioa'];
console.log(0 in arr2) //true
console.log('jie' in arr2) //falsemap
var arr2 = ['jie', 'bioa', 'nine'];
console.log(arr2.map(item => {
return item = "web"
})) (3) ["web", "web", "web"]
console.log(arr2.map(val => "web")) //(3) ["web", "web", "web"]数组转为字符串
join
var arr2 = ['jie', 'bioa', 'nine'];
console.log(arr2.join('|')) //jie|bioa|ninetoString
var arr2 = ['jie', 'bioa', 'nine'];
console.log(arr2.toString()) //jie,bioa,nine