How to solve the $ is not a function problem reported by js

Today, when I was working on a project, I encountered a very strange problem. I run a program in html well. If I run it in jsp project, the error $ is not a function is always reported. After searching for a long time, I tried a lot and did not solve it. Later, I suddenly thought about changing the order of the js files I introduced, and introducing the first js file of jquery, and putting other js files behind it. Solved the problem !!! It turns out that the imported files are loaded sequentially during page loading. If jquery's js file is not the first one to be introduced, the $. method name in other js will report an error. The $. method can be correctly executed only when jquery's js file is introduced first. Backup now!