- Shop NEW!
- The Vue Instance
- Template Syntax
- Computed Properties and Watchers
- Class and Style Bindings
- Conditional Rendering
- List Rendering
- Event Handling
- Form Input Bindings
- Reactivity in Depth
- Transition Effects
- Transitioning State
- Render Functions
- Custom Directives
- Single File Components
- Production Deployment Tips
- State Management
- Unit Testing
- Server-Side Rendering
- TypeScript Support
- Migration from Vue 1.x
- Migration from Vue Router 0.7.x
- Migration from Vuex 0.6.x to 1.0
- Comparison with Other Frameworks
- Join the Vue.js Community!
The Vue Instance
Every Vue vm is bootstrapped by creating a root Vue instance with the
Vue constructor function:
Although not strictly associated with the MVVM pattern, Vue’s design was partly inspired by it. As a convention, we often use the variable
vm (short for ViewModel) to refer to our Vue instances.
When you instantiate a Vue instance, you need to pass in an options object which can contain options for data, template, element to mount on, methods, lifecycle callbacks and more. The full list of options can be found in the API reference.
Vue constructor can be extended to create reusable component constructors with pre-defined options:
Although it is possible to create extended instances imperatively, most of the time it is recommended to compose them declaratively in templates as custom elements. We will talk about the component system in detail later. For now, you just need to know that all Vue components are essentially extended Vue instances.
Each Vue instance proxies all the properties found in its
It should be noted that only these proxied properties are reactive. If you attach a new property to the instance after it has been created, it will not trigger any view updates. We will discuss the reactivity system in detail later.
In addition to data properties, Vue instances expose a number of useful instance properties and methods. These properties and methods are prefixed with
$ to differentiate them from proxied data properties. For example:
Don’t use arrow functions on an instance property or callback (e.g.
vm.$watch('a', newVal => this.myMethod())). As arrow functions are bound to the parent context,
this will not be the Vue instance as you’d expect and
this.myMethod will be undefined.
Consult the API reference for the full list of instance properties and methods.
Each Vue instance goes through a series of initialization steps when it is created - for example, it needs to set up data observation, compile the template, mount the instance to the DOM, and update the DOM when data changes. Along the way, it will also invoke some lifecycle hooks, which give us the opportunity to execute custom logic. For example, the
created hook is called after the instance is created:
There are also other hooks which will be called at different stages of the instance’s lifecycle, for example
destroyed. All lifecycle hooks are called with their
this context pointing to the Vue instance invoking it. You may have been wondering where the concept of “controllers” lives in the Vue world and the answer is: there are no controllers. Your custom logic for a component would be split among these lifecycle hooks.
Below is a diagram for the instance lifecycle. You don’t need to fully understand everything going on right now, but this diagram will be helpful in the future.