vuejs
vue-loader 
webpack loader for Vue Single-File Components
v17.2.1+ Only Options
experimentalInlineMatchResource: boolean: enable Inline matchResource for rule matching for vue-loader.
v16+ Only Options
reactivityTransform: boolean: enable Vue Reactivity Transform (SFCs only).refSugar: boolean: removed. usereactivityTransforminstead.customElement: boolean | RegExp: enable custom elements mode. An SFC loaded in custom elements mode inlines its<style>tags as strings under the component'sstylesoption. When used withdefineCustomElementfrom Vue core, the styles will be injected into the custom element's shadow root.- Default is
/\.ce\.vue$/ - Setting to
truewill process all.vuefiles in custom element mode.
- Default is
enableTsInTemplate: boolean(16.8+): allow TS expressions in templates when<script>haslang="ts". Defaults totrue.When used with
ts-loader, due tots-loader's cache invalidation behavior, it sometimes prevents the template from being hot-reloaded in isolation, causing the component to reload despite only the template being edited. If this is annoying, you can set this option tofalse(and avoid using TS expressions in templates).Alternatively, leave this option on (by default) and use
esbuild-loaderto transpile TS instead, which doesn't suffer from this problem (it's also a lot faster). However, do note you will need to rely on TS type checking from other sources (e.g. IDE orvue-tsc).
What is Vue Loader?
vue-loader is a loader for webpack that allows you to author Vue components in a format called Single-File Components (SFCs):
<template>
<div class="example">{{ msg }}</div>
</template>
<script>
export default {
data() {
return {
msg: 'Hello world!',
}
},
}
</script>
<style>
.example {
color: red;
}
</style>There are many cool features provided by vue-loader:
- Allows using other webpack loaders for each part of a Vue component, for example Sass for
<style>and Pug for<template>; - Allows custom blocks in a
.vuefile that can have custom loader chains applied to them; - Treat static assets referenced in
<style>and<template>as module dependencies and handle them with webpack loaders; - Simulate scoped CSS for each component;
- State-preserving hot-reloading during development.
In a nutshell, the combination of webpack and vue-loader gives you a modern, flexible and extremely powerful front-end workflow for authoring Vue.js applications.
How It Works
The following section is for maintainers and contributors who are interested in the internal implementation details of
vue-loader, and is not required knowledge for end users.
vue-loader is not a simple source transform loader. It handles each language blocks inside an SFC with its own dedicated loader chain (you can think of each block as a "virtual module"), and finally assembles the blocks together into the final module. Here's a brief overview of how the whole thing works:
vue-loaderparses the SFC source code into an SFC Descriptor using@vue/compiler-sfc. It then generates an import for each language block so the actual returned module code looks like this:// code returned from the main loader for 'source.vue' // import the <template> block import render from 'source.vue?vue&type=template' // import the <script> block import script from 'source.vue?vue&type=script' export * from 'source.vue?vue&type=script' // import <style> blocks import 'source.vue?vue&type=style&index=1' script.render = render export default scriptNotice how the code is importing
source.vueitself, but with different request queries for each block.We want the content in
scriptblock to be treated like.jsfiles (and if it's<script lang="ts">, we want to to be treated like.tsfiles). Same for other language blocks. So we want webpack to apply any configured module rules that matches.jsalso to requests that look likesource.vue?vue&type=script. This is whatVueLoaderPlugin(src/plugins.ts) does: for each module rule in the webpack config, it creates a modified clone that targets corresponding Vue language block requests.Suppose we have configured
babel-loaderfor all*.jsfiles. That rule will be cloned and applied to Vue SFC<script>blocks as well. Internally to webpack, a request likeimport script from 'source.vue?vue&type=script'Will expand to:
import script from 'babel-loader!vue-loader!source.vue?vue&type=script'Notice the
vue-loaderis also matched becausevue-loaderare applied to.vuefiles.Similarly, if you have configured
style-loader+css-loader+sass-loaderfor*.scssfiles:<style scoped lang="scss">Will be returned by
vue-loaderas:import 'source.vue?vue&type=style&index=1&scoped&lang=scss'And webpack will expand it to:
import 'style-loader!css-loader!sass-loader!vue-loader!source.vue?vue&type=style&index=1&scoped&lang=scss'When processing the expanded requests, the main
vue-loaderwill get invoked again. This time though, the loader notices that the request has queries and is targeting a specific block only. So it selects (src/select.ts) the inner content of the target block and passes it on to the loaders matched after it.For the
<script>block, this is pretty much it. For<template>and<style>blocks though, a few extra tasks need to be performed:- We need to compile the template using the Vue template compiler;
- We need to post-process the CSS in
<style scoped>blocks, aftercss-loaderbut beforestyle-loader.
Technically, these are additional loaders (
src/templateLoader.tsandsrc/stylePostLoader.ts) that need to be injected into the expanded loader chain. It would be very complicated if the end users have to configure this themselves, soVueLoaderPluginalso injects a global Pitching Loader (src/pitcher.ts) that intercepts Vue<template>and<style>requests and injects the necessary loaders. The final requests look like the following:// <template lang="pug"> import 'vue-loader/template-loader!pug-loader!source.vue?vue&type=template' // <style scoped lang="scss"> import 'style-loader!vue-loader/style-post-loader!css-loader!sass-loader!vue-loader!source.vue?vue&type=style&index=1&scoped&lang=scss'