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？
if
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"}]
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。
JSON.stringify
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; },
