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 Vue provides us with a property to manipulate dom, ref. When bound to the dom element, it is used similar to the id. It is called through this.$refs, and it can also be bound to the component. It is very troublesome to obtain DOM elements in the previous native way. It needs to be obtained with such a long AP as: documentgetElementXXX/querySXXX.... Then jQuery was born to solve this pain point. The use of $("id") makes Our operation has become easier. But there are other problems, jQuery is just a library (plug-in) and cannot be used to build a framework. Now Vue can help us solve this problem. Vue also has its own method to obtain DOM, which is ref. It can get not only DOM elements but also components. If you add ref to the dom element, you can get the dom element, and if you add it to the component, you can get the component instance, and you can use the component method.

 The parent component uses props to pass data (such as a method) to the child component, and the child component needs to use custom events to pass data back to the parent component! We can use v-on to bind custom events, and then pass them to subcomponents, which will call after receiving the method. Each Vue instance implements the Events interface, that is: use $on(eventName) to listen for events and $emit(eventName) to trigger events.