javascript jquery 检查 json var 是否存在
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jquery check if json var exist
提问by David
How can I with jquery check to see if a key/value exist in the resulting json after a getJSON?
如何使用 jquery 检查在 getJSON 之后生成的 json 中是否存在键/值？
function myPush(){
$.getJSON("client.php?action=listen",function(d){
d.chat_msg = d.chat_msg.replace(/\\"/g, "\"");
$('#display').prepend(d.chat_msg+'<br />');
if(d.failed != 'true'){ myPush(); }
});
}
Basically I need a way to see if d.failed exist and if it = 'true' then do not continue looping pushes.
基本上我需要一种方法来查看 d.failed 是否存在，如果它 = 'true' 然后不要继续循环推送。
回答by beatgammit
You don't need jQuery for this, just JavaScript. You can do it a few ways:
为此，您不需要 jQuery，只需要 JavaScript。您可以通过以下几种方式做到这一点：
typeof d.failed- returns the type ('undefined', 'Number', etc)d.hasOwnProperty('failed')- just in case it's inherited'failed' in d- check if it was ever set (even to undefined)
typeof d.failed- 返回类型（'undefined'、'Number'等）d.hasOwnProperty('failed')- 以防万一它被继承'failed' in d- 检查它是否曾经设置过（甚至未定义）
You can also do a check on d.failed: if (d.failed), but this will return false if d.failed is undefined, null, false, or zero. To keep it simple, why not do if (d.failed === 'true')? Why check if it exists? If it's true, just return or set some kind of boolean.
您还可以对 d.failed: 进行检查if (d.failed)，但如果 d.failed 未定义、null、false 或零，这将返回 false。为简单起见，为什么不这样做if (d.failed === 'true')？为什么要检查它是否存在？如果是真的，只需返回或设置某种布尔值。
Reference:
参考：
http://www.nczonline.net/blog/2010/07/27/determining-if-an-object-property-exists/
http://www.nczonline.net/blog/2010/07/27/determining-if-an-object-property-exists/
回答by dexter
Found this yesterday. CSS like selectors for JSON
昨天发现了这个。类似 CSS 的 JSON 选择器
回答by Spoike
You can use a javascript idiom for if-statements like this:
您可以将 javascript 习惯用法用于 if 语句，如下所示：
if (d.failed) {
// code in here will execute if not undefined or null
}
Simple as that. In your case it should be:
就那么简单。在您的情况下，它应该是：
if (d.failed && d.failed != 'true') {
myPush();
}
Ironically this reads out as "if d.failed exists and is set to 'true'" as the OP wrote in the question.
具有讽刺意味的是，正如 OP 在问题中所写的那样，这读作“如果 d.failed 存在并设置为‘真’”。
