当我们对参数的个数不确定时,可以用对象拓展运算符
funtion lala(...arg){
console.log(arg[0]); 1
console.log(arg[1]); 2
console.log(arg[2]); 3
console.log(arg[3]); undefined
}
lala(1,2,3);
let arr1 = ['aaa','lala','con'];
let arr2 = arr1;
console.log(arr2); ['aaa','lala','con'];
arr2.push('chengdu');
console.log(arr1) ['aaa','lala','con','chengdu'];
引用导致.我们不想改变arr1
可用对象扩展符来实现
let arr1 = ['aaa','lala','con'];
let arr2 = [...arr1]; //把arr1数组的每个元素给arr2
console.log(arr2); ['aaa','lala','con'];
arr2.push('chengdu');
console.log(arr2); ['aaa','lala','con','chengdu'];
console.log(arr1) ['aaa','lala','con']; //达到目的，没有改变arr1 ,
rest运算符
rest 剩余的意思 就是剩余的参数
function lalaJs(first,...arg){
console.log(arg.length); 5
}
lalaJs(1,2,3,4,5,6);
function lalaJs(first,...arg){
for(let i = 0; i<arg.length;i++){
console.log(arg[i]); 2,3,4,5,6
}
这中循环 影响效率 有更好的是用for of 来写循环
for(let val of arg){
console.log(val)； 2 3 4 5 6
}
}
lalaJs(1,2,3,4,5,6);