var a = [1,2,3];
var b=[4,5]
a = a.concat(b);
console.log(a);
//此处输出为 [1, 2, 3 ,4 ,5]

// ES5 的写法
var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
Array.prototype.push.apply(arr1, arr2);
console.log(arr1)//[0,1,2,3,4,5]

// ES6 的写法
var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
arr1.push(...arr2);
console.log(arr1)//[0,1,2,3,4,5]

// ES6 的写法
var arr1 = [0, 1, 2];
var arr2 = [3, 4, 5];
var arr3=[...arr1, ...arr2]
console.log(arr3)//[0,1,2,3,4,5]