javascript 比较两个 json 数组

Comparing two json arrays

提问by Get Off My Lawn

I have this interval, that does an ajax request, currently every 5 seconds. I am having an issue with the ifstatement. my code ALWAYS enters it, and the two json values are the exact same, why is it seeing them as different?

我有这个间隔，它做一个 ajax 请求，目前每 5 秒一次。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);

Edit
Here is the console output (dashed line is to separate requests, it isn't in the actual output)

编辑
这里是控制台输出（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"}]

回答by Juan Mendes

JSON objects are not guaranteed to be serialized the same way, properties are not guaranteed to be in the same order, using JSON.stringifyis not a good way to test object equality.

不保证 JSON 对象以相同的方式序列化，不保证属性的顺序相同，使用JSON.stringify不是测试对象相等性的好方法。

A better example is a function like (found on the internet a while ago, wish I could give credit to the original author)

一个更好的例子是这样的函数（不久前在互联网上找到的，希望我能感谢原作者）

/**
 * 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;
},

回答by Strille

One solution would be to read the json data as text instead of json, and on success you check if the response string from the server differs from the last response string. Then you can call JSON.parse on the string. But this makes the comparison much easier and should only need a slight modification of your code.

一种解决方案是将 json 数据作为文本而不是 json 读取，并在成功时检查来自服务器的响应字符串是否与最后一个响应字符串不同。然后你可以在字符串上调用 JSON.parse。但这使得比较容易得多，并且只需要稍微修改您的代码。

回答by TaLha Khan

I think you should try comparing their properties.

我认为您应该尝试比较它们的属性。

for(var property in JSON.stringify(oldActivity))
    {
      if(JSON.stringify(oldActivity)[property]!=JSON.stringify(newActivity)[property])
                   $("#new-activity").slideDown( "fast" );
    }