Code _ javascript skills for determining whether a widget has been loaded

It is easy to determine whether a control has been loaded, that is, to use the browser's parsing sequence. In layman's terms, the higher the code is, the more loaded it is. For example:

The Code is as follows:

When parsing, the browser first loads the input tag and then the img tag.
If you want to determine whether the img tag is fully loaded, you can add a script before and after the img tag, for example
Code

The Code is as follows: