比较两个json数组

Question

我有这个间隔，当前每5秒执行一次ajax请求。我对if声明有疑问。我的代码总是输入它，并且两个json值完全相同，为什么它认为它们不同？

var newActivity = null, oldActivity = null;
setInterval(function(){
    $.ajax({
        type: "get",
        url: "/get/new_activity",
        dataType: "json",
        success: function(data){
            oldActivity = newActivity;
            newActivity = data;
            console.log(JSON.stringify(oldActivity));
            console.log(JSON.stringify(newActivity));
            if(JSON.stringify(oldActivity) != JSON.stringify(newActivity)){
                $("#new-activity").slideDown( "fast" );
            }
        }
    });
}, 5000);

编辑
这是控制台输出（虚线是分隔请求，它不在实际输出中）

null
[{"title":"How many planets are in the solar system?","title_url":"How-many-planets-are-in-the-solar-system%3F","id":"2","answers":"1","asked":"2013-01-11 10:03:50","asked_pretty":"Today","activity":"2013-01-11 12:33:53","activity_pretty":"Today"},{"title":"Why is the sky blue?","title_url":"Why-is-the-sky-blue%3F","id":"1","answers":"1","asked":"2013-01-11 09:55:13","asked_pretty":"Today","activity":"2013-01-11 12:03:45","activity_pretty":"Today"}]

---------------------------------------------------

[{"title":"How many planets are in the solar system?","title_url":"How-many-planets-are-in-the-solar-system%3F","id":"2","answers":"1","asked":"2013-01-11 10:03:50","asked_pretty":"Today","activity":"2013-01-11 12:33:53","activity_pretty":"Today"},{"title":"Why is the sky blue?","title_url":"Why-is-the-sky-blue%3F","id":"1","answers":"1","asked":"2013-01-11 09:55:13","asked_pretty":"Today","activity":"2013-01-11 12:03:45","activity_pretty":"Today"}]
[{"title":"How many planets are in the solar system?","title_url":"How-many-planets-are-in-the-solar-system%3F","id":"2","answers":"1","asked":"2013-01-11 10:03:50","asked_pretty":"Today","activity":"2013-01-11 12:33:53","activity_pretty":"Today"},{"title":"Why is the sky blue?","title_url":"Why-is-the-sky-blue%3F","id":"1","answers":"1","asked":"2013-01-11 09:55:13","asked_pretty":"Today","activity":"2013-01-11 12:03:45","activity_pretty":"Today"}]

---------------------------------------------------

[{"title":"How many planets are in the solar system?","title_url":"How-many-planets-are-in-the-solar-system%3F","id":"2","answers":"1","asked":"2013-01-11 10:03:50","asked_pretty":"Today","activity":"2013-01-11 12:33:53","activity_pretty":"Today"},{"title":"Why is the sky blue?","title_url":"Why-is-the-sky-blue%3F","id":"1","answers":"1","asked":"2013-01-11 09:55:13","asked_pretty":"Today","activity":"2013-01-11 12:03:45","activity_pretty":"Today"}]
[{"title":"How many planets are in the solar system?","title_url":"How-many-planets-are-in-the-solar-system%3F","id":"2","answers":"1","asked":"2013-01-11 10:03:50","asked_pretty":"Today","activity":"2013-01-11 12:33:53","activity_pretty":"Today"},{"title":"Why is the sky blue?","title_url":"Why-is-the-sky-blue%3F","id":"1","answers":"1","asked":"2013-01-11 09:55:13","asked_pretty":"Today","activity":"2013-01-11 12:03:45","activity_pretty":"Today"}]

Answer 1

不能保证以相同的方式序列化JSON对象，也不能保证属性以相同的顺序进行序列化，使用JSON.stringify并不是测试对象相等性的好方法。

一个更好的例子是这样的函数（前一段时间在互联网上找到，希望我能感谢原始作者）

/**
 * Deep compare of two objects.
 *
 * Note that this does not detect cyclical objects as it should.
 * Need to implement that when this is used in a more general case. It's currently only used
 * in a place that guarantees no cyclical structures.
 *
 * @param {*} x
 * @param {*} y
 * @return {Boolean} Whether the two objects are equivalent, that is,
 *         every property in x is equal to every property in y recursively. Primitives
 *         must be strictly equal, that is "1" and 1, null an undefined and similar objects
 *         are considered different
 */
function equals ( x, y ) {
    // If both x and y are null or undefined and exactly the same
    if ( x === y ) {
        return true;
    }

    // If they are not strictly equal, they both need to be Objects
    if ( ! ( x instanceof Object ) || ! ( y instanceof Object ) ) {
        return false;
    }

    // They must have the exact same prototype chain, the closest we can do is
    // test the constructor.
    if ( x.constructor !== y.constructor ) {
        return false;
    }

    for ( var p in x ) {
        // Inherited properties were tested using x.constructor === y.constructor
        if ( x.hasOwnProperty( p ) ) {
            // Allows comparing x[ p ] and y[ p ] when set to undefined
            if ( ! y.hasOwnProperty( p ) ) {
                return false;
            }

            // If they have the same strict value or identity then they are equal
            if ( x[ p ] === y[ p ] ) {
                continue;
            }

            // Numbers, Strings, Functions, Booleans must be strictly equal
            if ( typeof( x[ p ] ) !== "object" ) {
                return false;
            }

            // Objects and Arrays must be tested recursively
            if ( !equals( x[ p ],  y[ p ] ) ) {
                return false;
            }
        }
    }

    for ( p in y ) {
        // allows x[ p ] to be set to undefined
        if ( y.hasOwnProperty( p ) && ! x.hasOwnProperty( p ) ) {
            return false;
        }
    }
    return true;
},