How to add a class to another element when clicking on a button in Vue?

Question

Vue.js

How to add a class to another element when clicking on a button in Vue, for example, on the body when clicking on the button, the active class is hung?

Answer 1

for example on body

Since body should not be used as the root element of the application, it's the same as without vue - by directly accessing classList :
<button @click="onClick">

methods: {
  onClick() {
    document.body.classList.toggle('active');
  },
},

If not "for example" - read the documentation, everything is there.