Suffix on the extension of JS file is what file [original]_ Basics

A lot of friends just began to contact the network, do not know the suffix for JS file, what file, in fact, this extension is a. js file is a JavaScript file, why use <script src= "Test.js" ></script> Format to call the file, in fact, we often in the process of doing web pages, because the JS file if written to the Web page, not conducive to our repeated changes, if we need to modify the JS file, you can directly change the JS file, do not need to change the entire Web page, now everyone's website is to generate static HTML, If you want to modify thousands of static pages, whether it is to replace or save the site space, is a good choice.
Need to note that our JS file can only be JS grammar things, can not be simple text, I hope that the first contact with this aspect of the brothers, and more to join