“$attrs is readonly”,“$listeners is readonly”,“Avoid mutating a prop directly”

Question

I am new to Vue. I am trying to develop a chatting application where friend list will be shown on the left menu and the chat box will be shown at the body. I am loading frie

Answer 1

First, these errors only come out in non-production builds, however they indicate a problem that should be resolved before production release.

The $attrs, $listeners and other warnings are displayed if there's more than one instance of Vue loaded. As I understand it, this can happen usually for one these reasons:

• it is being loaded/packed into the bundle by webpack and also loaded externally (not via webpack)
• it is being loaded by something you include (e.g. vuetify, vue-test-utils, vue-cli-electron-builder) one way and by your webpack config another way (e.g. absolute vs relative paths, common.js vs esm.js vue files, runtime-only vue vs compiler+runtime vue)

If you click on that line (it was app.js:19302 in your output above) and put a breakpoint where the message is coming out, you can see the list of modules in the stack traceback to see if there's more than one path to Vue listed. For example, see that the top three modules have a different path below (but are all part of Vue): If you see Vue showing up in two or more different ways, it demonstrates that more than one instance of Vue is loaded. Vue only supports a single instance, and can produce these error messages if more than one is loaded.

There are several links to issues included above, the Vuetify issue was the one I filed. In that case, Vuetify requires Vue and was loading it differently than I was. Usually the fix is to check your webpack config where Vue is specified (or isn't) and try to make it match the way the other copy is being included (e.g. absolute vs relative path, or packed vs external).