In PHP when we include code from another file, we include it and that's it, the code is now available to us within the file in which we performed the include. But in Vue.js, after importing a component we must also export it.
Why? Why don't we simply import it?
in Vue.js, after importing a component we must also export it.
I think you might be referring to the following lines in User.vue and wondering why UserDetail and UserEdit are imported into the file and then exported in the script export's components property:
import UserDetail from './UserDetail.vue';
import UserEdit from './UserEdit.vue';
export default {
components: {
appUserDetail: UserDetail,
appUserEdit: UserEdit
}
}
vue-loader expects the script export of a .vue file to contain the component's definition, which effectively includes a recipe to assemble the component's template. If the template contained other Vue components, the definition of the other components would need to be provided, otherwise known as component registration. As #Sumurai8 indicated, the import of the .vue files itself does not register the corresponding single-file-components; rather those components must be explicitly registered in the importer's components property.
For example, if App.vue's template contained <user /> and User.vue were defined as:
<template>
<div class="user">
<app-user-edit></app-user-edit>
<app-user-detail></app-user-detail>
</div>
</template>
<script>
export default {
name: 'user'
}
</script>
...the User component would be rendered blank, and you would see the following console errors:
[Vue warn]: Unknown custom element: <app-user-edit> - did you register the component correctly? For recursive components, make sure to provide the "name" option.
[Vue warn]: Unknown custom element: <app-user-detail> - did you register the component correctly? For recursive components, make sure to provide the "name" option.
demo 1
When Vue attempts to render <user /> inside App.vue's template, Vue doesn't know how to resolve the inner <app-user-detail> and <app-user-edit> because their component registrations are missing. The errors can be resolved by local component registration in User.vue (i.e., the components property shown above).
Alternatively, the errors can be resolved with global component registration of UserDetail and UserEdit, which would obviate the local registration in User.vue. Note that global registration must be done before creating the Vue instance. Example:
// main.js
import Vue from 'vue';
import UserDetail from '#/components/UserDetail.vue';
import UserEdit from '#/components/UserEdit.vue';
Vue.component('app-user-detail', UserDetail);
Vue.component('app-user-edit', UserEdit);
new Vue(...);
demo 2
Components in vue can be tricky. If you haven't yet, I would highly recommend reading the documentation on the vue.js website on how component registration works, specifically, as tony19 mentions global and local registration. The code example you show in your screenshot is actually doing a couple of things. For one, it is making the components available locally, and only locally (as in that .vue file) for use. In addition, it is making it available to the template as the key you provide in the components object, in this case, app-user-detail and app-user-edit instead of user-detail and user-edit.
Importantly, it should be mentioned that an import is not actually required for this component registration to function. You could have multiple components defined in a single file. The components key gives a way to identify what that component is using. So that import isn't required, so vue does require the components key to understand what you are using as a component, and what is just other code.
Finally, as some of the other answers have alluded to, the components key is not actually an export. The default signature of a vue component requires an export but this is not exporting the components listed under the components key. What it is doing is letting vue build in a top down manner. Depending on what the rest of your application setup looks like, you may be using single file components, or not. Either way, vue will start with the top level vue instance and work its way down through components, with the exception of global registration, no top level component knows which components are being used below it.
This means for vue to render things properly, each component has to include a reference to the extra components it uses. This reference is exported as part of the higher level component (in your case User.vue), but is not the component itself (UserDetail.vue).
So it may appear that vue requires a second export after import, but it is actually doing something else to allow the root vue instance to render your component.
As an aside, the vue documentation on this subject really is quite good, if you haven't already please take a look at the sections I linked above. There is an additional section on module import/export systems that seems highly relevant to what you are asking, you can find that here: Module-systems.
import imports code into the current file, but it does not do anything on its own. Imagine the following non-vue code:
// File helpers.js
export function tickle(target) {
console.log(`You tickle ${target}`)
}
// File main.js
import { tickle } from 'helpers'
You have imported the code, but it does not do anything. To actually tickle something, you need to call the function.
tickle('polar bear');
In Vue this works the same. You define a component (or actually just an Object), but the component does not do anything on it's own. You export this component so you can import it in other places where the Vue library can do something with this object.
In a Vue component you export your current component, and import components you use in your template. You generally do the following:
<template>
<div class="my-component">
<custom-button color="red" value="Don't click me" #click="tickle" />
</div>
</template>
<script>
import CustomButton from './CustomButton';
export default {
name: 'my-component',
components: {
CustomButton
}
}
</script>
Your component mentions a component named "custom-button". This is not a normal html element. It does not know what to do with it normally. So what do we do? We import it, then put it in components. This maps the name CustomButton to the component you imported. It now knows how to render the component.
The "magic" happens when you mount the root component using Vue, usually in your main.js.
import Vue from "vue";
import App from "./App";
Vue.config.productionTip = false;
/* eslint-disable no-new */
new Vue({
el: "#app",
components: { App },
template: "<App/>"
});
What does this do? You tell Vue to render <App/> in a html element identified by #app, and you tell that it should find this element in ./App.vue.
But can't we just omit export if the Vue compiler was 'smarter'? Yes, and no. Yes, because a compiler can transform a lot of things into valid javascript, and no because it makes no sense and severely limits what you can do with your component, while also making the compiler more bug-prone, less understandable and overall less useful.
In order for App.vue to be able to use the User-component you need to export the default object of the User.vue-file.
In the export default { you don't actually export the newly imported components. You are just exporting a completely normal JavaScript Object. This object just happens to have a reference to another Object.
When you import an object (or function or array or ...) it does not actually load the content of that file in to your component like PHP. It simply makes sure that your compiler (probably webpack) knows how to structure the program. It basically creates a reference so webpack knows where to look for functionality.
TL;DR
The import and export here are conceptually different and unrelated things, and both have to be used.
Importing a Vue component is the same with any other importing in JavaScript:
// foo.mjs
export function hello() {
return "hello world!";
}
// bar.mjs
import { hello } from './foo.mjs';
console.log(hello());
Now run node bar.mjs, you will get a feeling how the importing works -- you want to use something that is defined/implemented somewhere else, then you have to import it, regardless of whether it is a Vue component or not.
With regard to export, you are not exporting the components you imported. The only thing you are exporting is the current component. However, this current component may use some other subcomponents in its <template>, so one has to register those subcomponents, by specifying them in the components field in the exported object.
Related
I have a Vue component that I just converted to class syntax. I have done this to three other components in my project with no problem. My component looks like this after reducing it to just the problematic code and no cruft:
<template>
<v-container>
blah
</v-container>
</template>
<script>
import { Vue, Component } from 'vue-property-decorator'
#Component({
})
export default class extends Vue {
}
</script>
And I get this error message dynamically in the browser console.
[Vue warn]: Invalid component name: "_class2". Component names should conform to valid custom element name in html5 specification.
I obviously haven't named anything _class2 here. Vue must have done that for me. Why is the name invalid? How do I pick a valid name?
The class needs to have a name given to it.
export default class Foo extends Vue {
Apparently if you don't do this, it'll work just fine, but randomly give it a name that quite possibly won't work. This is a case of frameworks building on top of Javascript and not being able to report errors at the level the programmer is writing code at, but the level of the generated Javascript instead.
When I search for something I came across this post
Here, something, I believe it is component, is defined as below.
export default {
name: 'app',
methods: {
testFunction: function (event) {
console.log('test clicked')
}
},
components: {
Test
}
}
As per the documentation, I came across this
import BaseButton from './BaseButton.vue'
import BaseIcon from './BaseIcon.vue'
import BaseInput from './BaseInput.vue'
export default {
components: {
BaseButton,
BaseIcon,
BaseInput
}
}
I really not sure, whether app is a component which contains Test. Is it the component definition in export? How do we understand that is a component from vue code?
Is it only by the below ways?
Vue.component
components in Vue instance
Not sure - the export default way?
I understand that I sound different because it is Javascript. Could someone help me with this?
There are conventionally, three different types of components in Vue JS.
Root Component
View Component
Normal Component
In a conventional structure the Root component is named 'app' and is passed to the Vue instance when initializing the App for the first time. This component can not be imported and reused inside other components as it will cause a recursive effect. For example this App.vue file is a Root component. It is used inside this main.js file and passed to the Vue instance using new Vue.
The View components are dynamically added or removed from the Root component based on the route. They are written and act as normal component and are only used for Vue router component property. For example the Home and Comments components inside this Router index file are known as View components. They are passed inside the route objects as components inside individual routes. When the app navigates to that particular route, the <router-view> template inside the App.vue file gets replace with the template of the corresponding View component.
Normal components can be used anywhere and are imported by other components. They can be imported inside the View components as well as the Root components. For example, in root component App.vue we see the component Navbar is used. In View component Comments.vue the Replies component is used.
All these components are identical in declaration and behavior but differ in usage.
In order to use a dynamically-defined single page component, we use the component tag, thusly:
<component v-bind:is="componentName" :prop="someProperty"/>
...
import DynamicComponent from '#/components/DynamicComponent.vue';
...
components: {
DynamicComponent
},
props: {
componentName: String,
someProperty: null,
}
The problem is, this isn't really very dynamic at all, since every component we could ever possibly want to use here needs to be not only imported statically, but also registered in components.
We tried doing this, in order at least to avoid the need to import everything:
created() {
import(`#/components/${this.componentName}.vue`);
},
but of course this fails, as it seems that DynamicComponent must be defined before reaching created().
How can we use a component that is truly dynamic, i.e. imported and registered at runtime, given only its name?
From the documentation: Emphasis mine
<!-- Component changes when currentTabComponent changes -->
<component v-bind:is="currentTabComponent"></component>
In the example above, currentTabComponent can contain either:
the name of a registered component,
or a component’s options object
If currentTabComponent is a data property of your component you can simply import the component definition and directly pass it to the component tag without having to define it on the current template.
Here is an example where the component content will change if you click on the Vue logo.
Like this:
<component :is="dynamic" />
...
setComponentName() {
this.dynamic = () => import(`#/components/${this.componentName}.vue`);
},
Solution for Nuxt only
As of now its possible to auto-import components in Nuxt (nuxt/components). If you do so, you have a bunch of components ready to be registered whenever you use them in your vue template e.g.:
<MyComponent some-property="some-value" />
If you want to have truly dynamic components combined with nuxt/components you can make use of the way Nuxt prepares the components automagically. I created a package which enables dynamic components for auto-imported components (you can check it out here: #blokwise/dynamic).
Long story short: with the package you are able to dynamically import your components like this:
<NuxtDynamic :name="componentName" some-property="some-value" />
Where componentName might be 'MyComponent'. The name can either be statically stored in a variable or even be dynamically created through some API call to your backend / CMS.
If you are interested in how the underlying magic works you can checkout this article: Crank up auto import for dynamic Nuxt.js components
According to the official Documentation: Starting from v2.13, Nuxt can auto import your components when used in your templates, to activate this feature, set components: true in your configuration
you are talking about async components. You simply need to use the following syntax to return the component definition with a promise.
Vue.component('componentName', function (resolve, reject) {
requestTemplate().then(function (response) {
// Pass the component definition to the resolve callback
resolve({
template: response
})
});
})
Usually I use a js code with functions to run on some events.
Now I am using nuxt.js and I wonder where to put this file or how to create a global method to use these functions in every component.
I could write the methods that I need inside every a specific component but after it wouldn't be usable outsite of it.
How to do that in vue/nuxt?
So one way to do it in vue.js is by using mixins, in nuxt you can also use mixins, then you should register them as plugins, but first:
Non global mixins
Create an extra folder for your mixins. For example in a /mixins/myMixin.js
export default {
methods: {
commonMethod() {
console.log('Hello')
}
}
}
Then import in a layout, page or component and add it via the mixins object:
<script>
import myMixin from '~/mixins/myMixin.js'
export default {
mixins: [myMixin]
}
</script>
Global mixins
For example in a new file plugins/mixinCommon.js:
import Vue from 'vue'
Vue.mixin({
methods: {
commonMethod() {}
}
})
Include the file in nuxt.config.js like that:
plugins: ['~/plugins/mixinCommon']
After that you would have the method everywhere available and call it there with this.commonMethod(). But here an advice from the vue.js docs:
Use global mixins sparsely and carefully, because it affects every
single Vue instance created, including third party components. In most
cases, you should only use it for custom option handling like
demonstrated in the example above. It’s also a good idea to ship them
as Plugins to avoid duplicate application.
I am trying to use vue-components in a webpack Typescript project but it doesn't seem to be working. I don't get any errors during the build and run, but the component HTML is never inserted into the output - I can just see the HTML source of the component instead i.e. .
My project is an ES2015 using Vue2 in VS.Net 2017. My component looks like this:
import Vue from 'vue'
import Component from 'vue-class-component'
// The #Component decorator indicates the class is a Vue component
#Component({
// All component options are allowed in here
template: '<button #click="onClick">Click!</button>'
})
export default class MyHeader extends Vue {
// Initial data can be declared as instance properties
message: string = 'Hello!'
// Component methods can be declared as instance methods
onClick(): void {
window.alert(this.message)
}
}
I have tried the official reference guide to register the component and use it. When I look at the vue-component example, it uses the same format as my project so I added the markup and properties to my Typescript class definition:
import Vue from 'vue';
import Component from 'vue-class-component';
import MyHeader from './MyHeader';
#Component({
components: {
MyHeader
}
})
export default class GetDataComponent extends Vue {
<...rest of class...>
}
but in my project the "components:" section is squiggly-underline-red with the message:
Object literal may only specify known properties, but 'components'
does not exist in type 'VueClass'. Did you mean to write
'component'?
Every example I have seen with vue-component (such as this one) uses the "components:" option in the #Component to register and use their Vue component, but in my project it doesn't seem to like it. I have also tried global registration of the component (such as this one) which includes the line:
// Register the component globally
Vue.component(my-header', MyHeader)`
but in that case I get an error like this:
Type 'typeof MyHeader' is not assignable to type 'AsyncComponent'
The Vue file works (without the Component added) and all content is rendered correctly. It's getting the Component included that doesn't work - I either get Design-time errors per above, or nothing appears in the output at all.
Is my import wrong? Or the format of the #Component? I get the feeling I am doing something that is very basic, very wrong...