Javascript dynamically binds the SRC address of IMG

Today, I wrote this example sectionCode: The SCR address in the IMG mark needs to call the dynamic binding of the JavaScript function. The method is as follows:

When browsing the page, the SCR is still "javascript: functionname ()", which is not the value returned by the function, that is, the function is not executed.

I searched the internet and wrote it as follows:

The results are the same and cannot be bound. The final solution is as follows:

The cause is as follows: when the SRC address is incorrect, the onerror event will be triggered. At this time, IMG has initialized the event, so using this. SRC is valid, so you can call the JavaScript function to assign values to SRC.