Building deeply nested html with vue-cli takes forever

Question

I found that vue-cli (2.9.6, but 3.0.0 beta* has the same issue) \'s building process takes forever once the template\'s html gets relativelly deep.

For example, I j

Answer 1

I can reproduce the performance issue as you described (macOS High Sierra 10.13.4, Node 8.9.4 and 9.11.1). The issue also occurs with a newly created vue-cli 3.x project.

The hang is actually happening in prettier, called from vue-loader's template compiler. The nested <div>s are converted into JavaScript by vue-loader, and that becomes the following snippet:

var render = function () {var _vm=this;var _h=_vm.$createElement;var _c=_vm._self._c||_h;return _c('div',{attrs:{"id":"app"}},[_c('img',{attrs:{"src":require("./assets/logo.png")}}),_vm._v(" "),_c('router-view'),_vm._v(" "),_vm._m(0)],1)}
var staticRenderFns = [function () {var _vm=this;var _h=_vm.$createElement;var _c=_vm._self._c||_h;return _c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div',[_c('div')])])])])])])])])])])])])])])])])])])])])])])])])}]

vue-loader passes this long string to prettier, which takes about 159 seconds to process. The cause of the bug is the deeply nested function calls that create the divs. I've reported this bug in prettier (Issue 4672).

In the meantime, I recommend refactoring your HTML to avoid deep nesting. If you need to stick with the old template, you could workaround the issue by building in production mode, as vue-loader skips prettier for production builds:

NODE_ENV=production npm run dev

UPDATE vue-loader v15.5.0 adds the prettify option to allow disabling prettier (update to the latest version of @vue/cli to ensure your vue-loader is current with the new option). You can use this option as follows:

1. Add vue.config.js (if it doesn't exist already) to the root of your project.

2. Edit the file to include:

   module.exports = {
     chainWebpack: config => {
       config.module
         .rule('vue')
         .use('vue-loader')
           .loader('vue-loader')
           .tap(options => {
             options.prettify = false
             return options
           })
     }
   }
   

Answer 2

Update 2019

Recently vue-loader added a flag in their options in order to disable prettier also during development.

Just add prettify: false to your vue-loader options.

https://vue-loader.vuejs.org/options.html#prettify

Notice: Just make sure you have the latest vue-loader version

Answer 3

I do not have any particular issue with your 25 nested <div>'s: (below example with Vue runtime compiler, so that you can easily test it directly in your browser)

new Vue({
  el: '#app',
  template: '#app-template',
});

#app div {
  border: 1px solid grey;
  padding: 1px;
}

<script src="https://unpkg.com/vue@2"></script>

<div id="app">
</div>

<template id="app-template">
<div id="app">
  <div>
    <div>
      <div>
        <div>
          <div>
            <div>
              <div>
                <div>
                  <div>
                    <div>
                      <div>
                        <div>
                          <div>
                            <div>
                              <div>
                                <div>
                                  <div>
                                    <div>
                                      <div>
                                        <div>
                                          <div>
                                            <div>
                                              <div>
                                                <div>
                                                  <div>25 nested <code>&lt;div&gt;</code>'s</div>
                                                </div>
                                              </div>
                                            </div>
                                          </div>
                                        </div>
                                      </div>
                                    </div>
                                  </div>
                                </div>
                              </div>
                            </div>
                          </div>
                        </div>
                      </div>
                    </div>
                  </div>
                </div>
              </div>
            </div>
          </div>
        </div>
      </div>
    </div>
  </div>
  </div>
</template>

Here is a demo with a Vue CLI project on CodeSandbox, probably closer to your example: https://codesandbox.io/s/v3knpl447l

(i.e. it precompiles the templates, so the building process actually happens on CodeSandbox server)

Answer 4

I had similar issues with vue-cli 3.1.1 (TypeScript + SCSS) and Bootstrap (which by default requires some nesting). Example structure:

<template>
    <div class="container">
        <div class="row">
            <div class="col-12">
                <div class="card-deck">
                    <div class="card">
                        <div class="card-body">
                            <div class="accordion">
                                <div class="card">
                                    <div class="card-header">
                                        ...
                                    </div>
                                    <div class="collapse">
                                        <div class="card-body">
                                            <div class="row">
                                                <div class="col-12 form-group">
                                                    <label>...</label>
                                                    <div class="dropdown">
                                                        <button class="custom-select" type="button" data-toggle="dropdown">{{someValue}}</button>
                                                        <div class="dropdown-menu">
                                                            <a class="dropdown-item" href="#" :data-key="somekey1" @click="onClickMethod">value1</a>
                                                            <a class="dropdown-item" href="#" :data-key="somekey2" @click="onClickMethod">value2</a>
                                                            ...

needed ~12 seconds to compile 400+ lines of code (template + TypeScript + SCSS). After removing:

:data-key="somekey1" @click="onClickMethod"
:data-key="somekey2" @click="onClickMethod"

the code needed ~5-6 seconds to compile. After moving the code to custom component (and some TypeScript code from Vue component to Helper.ts file):

<template>
    <div class="container">
        <div class="row">
            <div class="col-12">
                <div class="card-deck">
                    <div class="card">
                        <div class="card-body">
                            <div class="accordion">
                                <div class="card">
                                    <div class="card-header">
                                        ...
                                    </div>
                                    <div class="collapse">
                                        <div class="card-body">
                                            <SubComponent/>

it needs ~700ms to compile (one main component and two additional sub-components, each file having less than 100 lines of code + Helper.ts having exactly 97 lines of code).

So if you suffer from poor npm run serve performance, try sub-components first, I didn't noticed much difference in compile time while invoking npm run build so I assume (maybe incorrectly) that this problem is also caused by code prettifier which is enabled for serve but disabled for build (TSLint is not invoked on save action so it does not affect npm run serve in my case).