let sum=(...m)=>{
    console.log(m[0]);   //经判断m为数组   console.log(m instanceof Array); } sum(1,2,3); //此时...为运算符将4和8进行拆解 // var [x,y]=[4,8]; console.log(...[4,8]); let arr1=[1,2],arr2=[4,8]; //[1, 2, 4, 8] console.log(arr1.concat(arr2)); //[1, 2, 4, 8] console.log([...arr1,...arr2]); var [x,...y]=[1,84,654,8,4]; //x=1,y=[84,654,8,4] var [a,b,c]="es6"; //a=e,b=s,c=6;   var xy=[..."es6"];   //xy=["e", "s", "6"]