javascript 为什么这个对象属性未定义？
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Why is this object property undefined?
提问by maxedison
Consider the code below. The first console.logcorrectly logs the image, and you can see its properties in the image below. However, when I try logging one if its properties to the console, I get undefined!
考虑下面的代码。第一个console.log正确记录图像，您可以在下图中看到其属性。但是，当我尝试将其属性记录到控制台时，我得到undefined!
console.log(that.data[0].cards); //works -- see image below
console.log(that.data[0].cards.E); //undefined
console.log(that.data[0].cards['E']); //undefined
console.log(that.data[0].cards.hasOwnProperty('E')); //false
var test = JSON.stringify(that.data[0]);
console.log(test); // {}
for( var key in that.data[0].cards ) {
console.log('hello????') //doesn't appear in the console
}
console.log( Object.keys( that.data[0].cards ) ); //[]
console.log( that.data[0].cards.propertyIsEnumerable("E") ); //false
console.log( that.data[0].cards.__lookupGetter__( "E" ) ); //undefined
The result in the console:
控制台中的结果：
Any idea what's going on here? The xmlproperty inside of that.data[0]should also have properties inside of it -- named the same, in fact, as the properties in cards.
知道这里发生了什么吗？该xml物业内that.data[0]也应该有它的内部性能-命名一样，其实，在属性cards。
FWIW, I get the same thing in Firebug (the above console image is Chrome).
FWIW，我在 Firebug 中得到了同样的东西（上面的控制台图像是 Chrome）。
回答by maxedison
I've solved the problem. Basically, the object in question (that.data[0].cards) has its properties created by a function a()that runs after all the AJAX requests for the necessary XML files have been processed. I allow the requests to run asynchronously, using a counter to determine in the successcallback function if a()should be called yet.
我已经解决了这个问题。基本上，所讨论的对象 ( that.data[0].cards) 的属性是由一个函数创建的，该函数a()在处理完对必需 XML 文件的所有 AJAX 请求之后运行。我允许请求异步运行，使用计数器在success回调函数中确定是否a()应该被调用。
After a()runs, function b()is supposed to perform operations on that.data[i].cards. However, b()was running prior to a()being called because of a()'s reliance on the asynchronous requests. So the solution was simply to make a()call b().
之后a()运行，功能b()应该执行的操作that.data[i].cards。但是，由于依赖于异步请求，b()因此在a()被调用之前正在运行a()。所以解决方案就是a()拨打 call b()。
So this turned out to be a pretty simple mistake on my part. What made it so confusing was the fact that logging that.data[0].cardsto the console showed me that in fact the cardsobject had already been built, when in fact it had not yet. So the console was providing me with incorrect--or at least unclear--information.
所以这对我来说是一个非常简单的错误。令人如此困惑的是，登录that.data[0].cards控制台向我显示该cards对象实际上已经构建，而实际上尚未构建。所以控制台向我提供了不正确的——或者至少是不清楚的——信息。
Thanks for everyone's help last night! Upvotes all around :)
谢谢大家昨晚的帮助！到处点赞:)
回答by Esailija
I think the object keys have unprintable characters, such can be replicated like this:
我认为对象键具有不可打印的字符，可以像这样复制：
var obj = {};
obj["E"+String.fromCharCode(15)] = new Array(15);
console.log(obj);
/*Object
E: Array[15]
__proto__: Object*/
console.log(obj.E)
//undefined
console.log( obj["E"+String.fromCharCode(15)] )
//[]
Edit: you can see if this is the case for your object keys:
编辑：您可以查看对象键是否属于这种情况：
var realKeys = [];
for( var key in obj ) {
realKeys.push( [].slice.call( key ).map( function(v){return v.charCodeAt(0);} ).join(" ") );
}
//["69 15"] (69 stands for the letter "E" and 15 was the unprintable character I added manually)
Edit2: Since you can't do that I came up with another way to see if there are unprintable characters:
Edit2：既然你不能这样做，我想出了另一种方法来查看是否有不可打印的字符：
Copypaste the key string like this: (go all the way as much as you can on both ends so you pick any invisible characters)
像这样复制粘贴关键字符串：（在两端尽可能多地走，这样你就可以选择任何不可见的字符）
Then dump your clipboard like this (Make sure you are using double quotes):
然后像这样转储剪贴板（确保使用双引号）：
