陣列和物件的拷貝

//淺拷貝
function shallowCopy(src){
    if(typeof src != 'object'){
        return src;
    }
    var dest = Array.isArray(src) ? [] : {};
    for(var p in src){
        if(src.hasOwnProperty(p)){
            dest[p] = src[p];
        }
    } 
    return dest;
}
//深拷貝
function deepCopy(src){
    if(typeof src != 'object'){
        return src;
    }
    var dest = Array.isArray(src) ? [] : {};
    for(var p in src){
        if(src.hasOwnProperty(p)){
            dest[p] = typeof(src[p]) == 'object' ? deepCopy(src[p]) : src[p];
        }
    }
    return dest;
}
//JSON.parse深拷貝,在基本型別的拷貝上夠用了
//缺點：不支援NaN，Infinity，精確的浮點數，function和迴圈引用, 屬性是undefined或null的時候會被移除掉
var obj2 = JSON.parse(JSON.stringify(obj));

//陣列淺拷貝
arr.slice(0)
arr.concat()
var [...arr2] = arr;

//物件淺拷貝
var {...obj2} = obj;
//Object.assign只對頂層屬性進行復制，並且是淺拷貝
var obj2 = Object.assign({},obj);