Summary of JS synchronization, asynchronous and lazy loading implementation

This time I will bring you a summary of the implementation of JS synchronization, asynchronous and delayed loading, and what are the precautions for the implementation of JS synchronization, asynchronous and delayed loading. The following is a practical case, let's take a look.

1: Synchronous loading

The most commonly used method.

<script src="http://yourdomain.com/script.js"></script>

Synchronous mode, also known as blocking mode , will prevent the browser from subsequent processing and stop subsequent parsing. Only when the current loading is completed, the next step can be performed. Therefore, synchronous execution is safe by default. But if there are behaviors such as outputting document content, modifying DOM, redirection, etc. in js, it will cause page congestion. Therefore, it is generally recommended to place the