As a newcomer to Vue, I've noticed that in many tutorials and documentation sources, the new Vue instance is often stored in a variable like app. I'm curious, what is the benefit of saving the Vue instance in a constant or variable?
const app = new Vue({
el: "#app",
components: {},
methods: {}
// options
})
The decision really depends on how you plan to use it.
One scenario might be that you have an existing app already live in production. In this case, you may only want to integrate Vue.js into certain sections of the app. It's even possible that you could have multiple instances of Vue running on the same page, so keeping references to them would be beneficial.
Another situation where saving a reference to a new Vue component is useful is when implementing a global event bus. This involves assigning a reference to a new Vue instance, like so:
Vue.prototype.$eventBus = new Vue();I believe I have a scenario that helps illustrate my question.
It's important to note that arrow functions cannot be used on certain properties or callbacks, like
created: () => console.log(this.a)vm.$watch('a', newValue => this.myMethod())this context, the keyword will be searched for in parent scopes, leading to potential errors such as
Uncaught TypeError: Cannot read property of undefined or Uncaught TypeError: this.myMethod is not a function.To work around this issue with data properties, one approach is to utilize an arrow function where the component's instance can still be accessed as the function's first argument:
var data = { a: 1 }
// Direct instance creation
var vm = new Vue({
data: data
})
vm.a // => 1
vm.$data === data // => true
// Function must be used with Vue.extend()
var Component = Vue.extend({
data: vm => ({ a: vm.myProp })
})
However, it's worth noting that this is not the conventional practice. Usually, data properties in components are declared as functions to allow direct access to the Vue instance.
// Must use function with Vue.extend()
var Component = Vue.extend({
data: function () {
return { a: 1 }
}
})
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