如何设置“if object exists”？条件？ [英] How do I setup an "if object exists" condition?

问题描述

有没有办法检查对象是否存在？我不断收到需要对象的错误。我知道该对象不存在，我想绕过我的代码的一部分，如果是这样的话。我不知道我还没有尝试过...

Is there some way to check if an object exists? I keep getting an "object required" error. I know the object does not exist and I would like to bypass a part of my code should that be the case. I don't know what I have not tried...

    var codeName = document.getElementById('testCode');
    //I have tried
    if(codeName != null)
    if(codeName.length != 0)
    if(typeOf codeName != 'undefined')
    if(!codeName)
    if(codeName.value != null)

是否有查看对象是否存在的任何方法？

Is there any way to see if an object exists?

推荐答案

getElementById 之后call， codeName 是一个DOM元素或null。您可以使用警报查看哪个：

After the getElementById call, codeName is either a DOM Element or null. You can use an alert to see which:

alert(codeName);

所以 if（codename！= null）应该工作。

错误是否会在它到达之前发生？我会尝试添加警报，以便在代码运行时查看值。或者在调试器中逐步执行此代码。

Does the error happen before it gets that far? I would try adding alerts to see the values as the code runs. Or step through this code in a debugger.

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