element.children 的 console.log 显示长度为 0，但稍后展开时包含三个条目

Question

In my JavaScript, I have two elements.

I have logged the two elements and it shows the following:

Element 1:

Element 2:

The problem is:

• When I console.log the children of each element ( element.children ) it obviously returns a list of elements.
• But the weird thing is, that one element is empty (and has a length of 0), but has 3 elements (and has a length of 3) once expanded.

If you read the logs below for the children of the elements, you will understand what I am talking about...

Element 1 (this one is working as expected):

Element 2 (the problematic one):

Does anyone have any idea what is going on here? How can there be contradictory reports of the number of children?

How do I fix this? I need to loop through the children, but it won't let me because the length is apparently 0.

Thanks in advance. All help appreciated.

Answer 1

When you log objects to the console, the object's current state is not snapshotted and displayed (as you might expect); instead, the console gets a live reference to the object. When you expand it in the console, you see its contents as of when you expand it , not as of when you logged it. More on that in this question and its answers .

So apparently your collections are empty when you do your logging, and then gain their elements later. You just want to make your code wait until the collections are populated. For instance, if you're doing this immediately when your script is run, consider putting the script at the end of the document, right before the closing </body> tag.

The very subtle blue (i) icon next to the object has a tooltip that's useful; if you hover it you see:

It says "Object value at left was snapshotted when logged, value below was evaluated just now."

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But generally: Rather than stumbling around in the dark with a console.log torch, I suggest turning on the lights using the debugger built into your browser and/or IDE.