JS 合并数组

var arr1=['a','b','c','d'];
var arr2=['d'];
var arr3=['e','f'];
var cc=arr1.concat(arr2,arr3);
console.log(cc);//["a", "b", "c", "d", "d", "e", "f"]

var arr1=['a','b','c','d'];
var arr2=['d'];
var arr3=['e','f'];
var dd=[...arr1,...arr2,...arr3];
console.log(dd);//["a", "b", "c", "d", "d", "e", "f"]