精致的JavaScript代码

1. 统计一个数组中，每个值的个数

var cards = [1, 2, 3, 4, 3, 2, 1, 4, 5]
var dict = {};

for(var i = 0; i < cards.length; i ++){
    dict[cards[i]] = dict[cards[i]] ? dict[cards[i]] + 1 : 1;
} 


console.log(dict);

// { '1': 2, '2': 2, '3': 2, '4': 2, '5': 1 }

2. 比较两个对象的内容是否相同

var compareOBJ = function (obj1, obj2) {
    var o1 = obj1 instanceof Object;
    var o2 = obj2 instanceof Object;

    if(!o1 || !o2)
        return obj1 === obj2;

    if(Object.keys(obj1).length !== Object.keys(obj2).length)
        return false;

    for(var attr in obj1) {
        var to1 = obj1[attr] instanceof Object;
        var to2 = obj2[attr] instanceof Object;

        if(to1 && to2) {
            compareOBJ(obj1[attr], obj2[attr]);
        }else if(obj1[attr] !== obj2[attr]) {
            return false;
        }
    }
    return true;
};