Vue is Not a Constructor

The error message “Vue is not a constructor” often occurs when trying to create a new Vue instance without properly importing or setting up Vue.js in your application. This error typically indicates that Vue.js is not available or has not been loaded correctly.

Here are some steps to resolve the “Vue is not a constructor” error:

Ensure Vue is Installed and Imported:
Make sure you have Vue.js installed as a dependency in your project and that you are importing it correctly in your application’s entry point (e.g., main.js or wherever you create Vue instances).
You can install Vue.js using npm: npm install vue

Then, ensure you import Vue at the top of your file where you create the Vue instance: import Vue from ‘vue’;

Check Vue Version Compatibility:

If you’re migrating from an older version of Vue to a newer one, be aware that there might be changes in the way Vue is imported or initialized. Ensure that the import method aligns with the version you’re using.
Like Vue import and instance creation process is different for the vue2 and vue3 versions like below.

V2:

import Vue from "vue";
let app = new Vue({
   el: "#app",
   data: {
       message: "Hello World!",
   },
});

 
V3:

import { createApp } from "vue";
createApp({
  data() {
     return {
        message: "Hello World!",
      };
  },
}).mount("#app");	

Check for Global Vue Overwriting:

Ensure that you are not accidentally reassigning or overwriting the Vue object elsewhere in your code. For example, reassigning Vue to something else before using it as a constructor could cause this error.

Verify Vue’s Loading Sequence:

Make sure that the script tag for Vue.js is included and loaded before any other script that tries to use Vue as a constructor. Ensure it’s included in your HTML before other scripts that depend on it.

Check for Vue.js CDN or External Sources:

If you are using a CDN link or external source for Vue.js, ensure that it is correct and accessible.