PWA and Lighthouse


Hello everyone,

I am trying to build a PWA using ionic.

I created a new project using sidemenu. After enabled service-workers, and run an audit with lighthouse, I get a lot of bad performance (main.css specialy)

To launch my PWA , I do :

npm run ionic:build --prod
ionic cordova emulate browser --livereload

And obtain this result :

My ionic info :

@ionic/cli-utils : 1.10.1
ionic (Ionic CLI) : 3.10.1

global packages:

Cordova CLI : 7.0.1

local packages:

@ionic/app-scripts : 3.1.0
Cordova Platforms  : browser 4.1.0
Ionic Framework    : ionic-angular 3.9.2


Node : v7.7.1
npm  : 4.1.2
OS   : Windows 10

Main.css is a generated file. so i can’t do this

Any help or suggestion would be great :slight_smile:
Thanks in advance


If you use ionic cordova emulate browser to serve your app, I think it will do a dev build. So to test the performance of a production build you have to run ionic build --prod and then serve the contents of www with some tool (or upload it to a server).

Regarding the file size of main.css, one easy thing you can do is remove all unused colors from the $colors array in src/theme/variables.scss. Ideally you will only have one or two colors left. This will reduce the file size already quite a bit. For more advanced stuff, see

Furthermore Ionic 4 will introduce lazy loading for css, which will bring further performance improvements and the steps from the post above will not be necessary anymore.

Hope that helps.


Here some additional tips that I applied to improving my Ionic PWA.

Yes, Ionic 4 will make life SOOOOO much better.


Thanks for your reply @ChrisGriiffith & @pwespi
When is ionic 4 released ?


No formal date has been announced for Ionic 4.


okk thnaks, i will follow this :slight_smile:

Really liked to lean angular, and applied it with ionic. I saw like ionic will give the choose of the framework when we create a new projectt, like read, angular… Right ?
Is there any article about new feature? I dont find


Hello All,

I want to share additional link for improving ionic pwa application performance.
I followed most of the directive in the above link and I achieved to increase the performance of my applications

I hope help others.