arguments对象接收所有实参

function fun() {
    console.log(arguments);
    console.log(arguments.length);

}
fun(1,2,3,4,5,6,7,8,9);

循环输出所有实参

    function fun() {
        console.log(arguments);
        console.log(arguments.length);




    for(var i = 0; i <= arguments.length -1 ;i++){

        console.log(arguments[i]);
    }

}
    fun(1,2,3,4,5,6,7,8,9);

根据传入参数的数量输出不同结果

function sum(a,b,c){

    switch(arguments.length){
        case 1:
            return a;
            break;

        case 2:
            return a + b;
            break;

        case 3:
            return a > b ? a + c : b + c ;
            break;

        default:
        throw new Error("参数个数不能超过3个");
    }
}

console.log(sum(1));
console.log(sum(1,2));
console.log(sum(1,2,3));
console.log(sum(1,2,3,4,5));