【前端】三种复制数组的方法

// 三种数组复制方法 

// 1. by slice 
var arr = [1, 2, 3], copyArr; 
copyArr = arr.slice(); 

// 2. by concat 
var arr = [1, 2, 3], copyArr; 
copyArr = arr.concat(); 

// 3. by loop 
var arr = [1, 2, 3], copyArr = []; 
for (var i = 0; i < arr.length; ++i) {
    copyArr.push(arr[i]);
}