How to write jquery and the difference between executing JS after the page is loaded_jquery

1. $(function(){
　$("#a").click(function(){
　　 //adding your code here
　});
});
2. $(document).ready(function(){
　$("#a").click(function(){
　　 //adding your code here　　
　});
});
3. window.onload = function(){
　$("#a").click(function(){
　　 //adding your code here
　});
}
The html code is click, and the page needs to reference the js file of jquery

The general method of calling js when loading a page is as follows:

This code will be executed after all documents on the entire page are loaded. Unfortunately, this method not only requires that the DOM tree of the page be fully loaded, but also requires that all external images and resources be loaded. What's even more unfortunate is that if external resources, such as images, take a long time to load, then this js effect will make the user feel ineffective.

But use the jquery method:

just needs to load all the DOM structures and execute the js effect before the browser puts all the HTML into the DOM tree. Included before loading external images and resources.

There is also a shorthand way: