javascript - The method in methods will get the value twice, the first time is empty

Question

I originally wanted to get the length of the reply, but the error message was always undefined, and the page was displayed normally, so I logged the value and looked at it and found that it was executed twice and the first time the value was empty. I don’t know what it was. Why, can anyone help me look at it?

Answer 1

It must have been called twice, check carefully

Answer 2

Then you have to check if you have called this method twice

Answer 3

Isn’t it normal to call it twice?

This will happen if you assign values ​​asynchronously