Will Browning.

3rd Jul 18 (Updated: 17th Jul 19) #nuxt 2 min read

Reducing the Vendor Bundle Size in Nuxt.js

When running Nuxt's "npm run generate" command I kept getting a warning stating that the javascript vendor bundle was too big on my static blog and that it was above the recommended 300kB size limit. Let's have a look at trying to reduce the size of it!

The warning in question looks like this:

Vendor Warning

Our vendor bundle is coming in at 752kB!

Identifying the Main Culprits

First things first we need to find out why our vendor bundle is so big in the first place.

Luckily Nuxt uses webpack-bundle-analyzer so we can simply add the following to our nuxt.config.js under the build property.

build: {
  analyze: true,

Then when you run npm run generate it will open up the build analyser at

Build Analyser

Looking at this we can see the highlight.js package is very big with a parsed size of 540kB!

If we inspect this further we can see this is mainly due to a few languages included with it like mathematica.js or sqf.js.

Now in my case I only use a handful of common languages so I don't need any of the other included ones.

Including Only Highlight.js Languages We Need

After a little bit of searching I came across this comment on GitHub on how to acheive this.

So let's give it a try and update our Nuxt site.

I have a filters.js in the plugins directory where I was importing highlight.js.

I updated the import to the following: (I was previously doing import hljs from 'highlight.js')

import hljs from 'highlight.js/lib/highlight.js'

Then simply specify which languages you want to register like so:

hljs.registerLanguage('php', require('highlight.js/lib/languages/php'))
hljs.registerLanguage('javascript', require('highlight.js/lib/languages/javascript'))
hljs.registerLanguage('css', require('highlight.js/lib/languages/css'))

Make sure to only add the languages that you intend to use.

Also Update Highlight.js In Build > Vendor

I also had Highlight.js in the vendor file importing all of the languages, so I simply updated this aswell:

build: {
  vendor: ['axios', 'highlight.js/lib/highlight.js'],
  analyze: true,
Note: The vendor array has been deprecated in Nuxt 2.0

Then ran npm run generate again and had a look at the build analyser.

The Result

This time the vendor bundle was only 226kB in parsed size, down from 752kB! That's a 70% decrease just from removing uneeded languages.

Build Analyser

As you can see we reduced the Highlight.js package down to 31.53kB from 540kB.

And since our vendor bundle is now less than 300kB we no longer get the annoying warning in our terminal. Success!

Another example we can use is with moment.js, which is usually overkill if you are only doing some basic date formatting.

Another library that is much more lightweight and has a similar API is day.js.

If we remove moment.js and run npm install dayjs --save to replace it with day.js then we can simply do the following:

const dayjs = require('dayjs')
import advancedFormat from 'dayjs/plugin/advancedFormat'

Vue.filter('toDate', function(timestamp) {
  return dayjs(timestamp*1000).format('Do MMM YY')

The reason we needed to import the advancedFormat plugin for day.js is simply because 'Do' is not included in the default day.js installation.

We can now format dates in the same way as with moment but using a much smaller library.

I'll try to add more examples here in the future.

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