var arr1 = ['red','green'];
var arr2 = arr1.slice(0);//複製
console.log(arr2)//['red','green'];
arr1.push('black') ;//改變color1的值
console.log(arr2)//["red", "green"]
console.log(arr1)//["red", "green", "black"]

var arr1 = ['red','green'];
var arr2 = arr1.concat();//複製
console.log(arr2)//['red','green'];
arr1.push('black') ;//
 
改變color1的值
console.log(arr2)//["red", "green"]
console.log(arr1)//["red", "green", "black"]

深拷貝：

var arr1 = ['red','green'];
var arr2 = JSON.parse(JSON.stringify(arr1));//複製
console.log(arr2)//['red','green'];
arr1.push('black') ;//改變color1的值
console.log(arr2)//["red", "green"]
console.log(arr1)//["red", "green", "black"]
 

function deepClone(obj){
    //判斷引數是不是一個物件
    let objClone = obj instanceof Object?[]:{};
    if(obj && typeof obj==="object"){
        for(key in obj){
            if(obj.hasOwnProperty(key)){
                //判斷ojb子元素是否為物件，如果是，遞迴複製
                if(obj[key]&&typeof obj[key] ==="object"){
                    objClone[key] 
 
= deepClone(obj[key]);
                }else{
                    //如果不是，簡單複製
                    objClone[key] = obj[key];
                }
            }
        }
    }
    return objClone;
}    

var a ={
    x:1,
    y:2
};


b=deepClone(a);
a.x=3
console.log(a);
console.log(b);