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How to implement the Composition API in Vue3

Educative Team


Until Vue 2, we only had one way of writing components in a Vue program. But, with improvements and up-gradation of Vue 2 to Vue 3, we can now write components differently using the Composition APIApplication Programming Interface.

Composition API

The Composition API allows developers to write code with more flexibility, and it allows users to integrate TypeScript with their program.

This API modifies the previously used Options API in Vue 2 and includes a relatively more straightforward way of writing data, computed, method, watches, etc.

Note: Check out the official documentation of Composition API here.

Composition API allows a user to write components and composition functions, such as mixinsA flexible way to distribute reusable functionalities for Vue components and scoped slotsA scoped slot functions as a reusable template (that can be passed data to) instead of already-rendered elements..


To install the Composition API in our Vue 2 or Vue 3 program, we execute the following command in our terminal.

npm install --save @vue/composition-api

If you don’t have npmnode package manager installed, then click here.


Let’s write a code example to understand the working of Composition API in Vue.

import Vue from 'vue'
import App from './App.vue'
Vue.config.productionTip = false
new Vue({
  render: h => h(App),


  • {{}}: These are place-holders used for data.
  • v-model: This is used for two-way binding. It binds the value of HTMLHyperText Markup Language elements to application data.

The main difference between the Options API in Vue 2 and Composition API in Vue 3 is the newly introduced setup() function inside export default. The setup() function is the starting point of this API and is executed right before the component is created. This function allows the reusability of certain components.

Code explanation

  • Lines 1–5: We have the <template> tag that includes a <div> element. This div takes input from the user and passes whatever is written inside the textbox. We can see this in the output above when we press “Run”.

  • Line 8: In order to use the ref, computed, or other methods, we have to define them. The import statement defines these methods so that we can use them in our code.

  • Line 11: Using the setup() function, we can make reactive states and standalone primitive values (such as strings, boolean, etc.) using reactive and ref methods, respectively.

  • Line 12: We use the day object, which passes the input value to ref using placeholders or {{}}.

  • Line 13: We use the computed() method. The computed() method is a new method introduced in Vue 3, which we can use to implement logic in our setup() function. Notice that we use day.value. This is because day has a type of ref, whereas in the <template> tag, the internal value is directly accessible.


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