29 Sep 2017

How we cut down our ember build time?

The journey starts about 4 months back when my ember build took even 2 mins (at worst case) to rebuild (incremental rebuild). You know it’s really painful 😰 when you need to wait for 2 mins to get your changes in the browser. So I decided to dive into the build process to know which of the build task took a long time to finish. Actually, there are many! Some of those are:

  • concating source maps for both app and test files
  • merging the trees and
  • few custom build tasks.

When examing the number, a task took almost half of the total build time 😱 and that was to concatenate the test files. The first question that knocks the door was

“Why the test files need to be concatenated during my development, where I know I will not touch a single test file at all?” 🤔

Yes, the answer is “You don’t need to!”. I was so relaxed that I can now eliminate half of my build time 😌. But, how? Zoooob! Headed towards the community and [this thread] (https://discuss.emberjs.com/t/excluding-test-related-files-when-building-for-environment-development/10232) helped me out. As mentioned, you can eliminate the test file manipulations by adding an option, tests: false to your build file (ember-cli-build.js) so that a sample build file will look like,

let EmberApp = require('ember-cli/lib/broccoli/ember-app');

module.exports = function(defaults) {

  let buildOptions = {};

  if ( process.env.EMBER_ENV === 'development') {
    // only during development mode
    buildOptions.tests = false;

  let app = new EmberApp(defaults, buildOptions);

  return app.toTree();

Awesome! we cut off our build to almost half but its almost a minute in worst cases. But far better than the earlier one. Days went good and on another fine day last week, I accidentally noticed that a task for concatenating source map of app files took a half part of the total build time. Again tools on the hand. Actually, I was not surprised at the numbers because our codebase is large and concatenating those files would take some time than usual. Just to have a look, I examined the source map file of our app and I once again stunned that about 15 percent of the file were from mirage folder where we have our mock-data files. Again the same question,

why those mirage files have to be included in the build when the test files itself eliminated (in the previous process)? 🤔🤔

Fortunately, again the answer was “Yes, don’t need to include”! Again a 15% reduction in sourceMapConcat time. That’s great, but how to exclude those files. Luckily, ember-cli-mirage has an option to exclude the files explicitly with a config option (config/environment.js). We need to set the flag, excludeFilesFromBuild to true for the development environment to exclude those files from the build (as the key itself is self-explanatory). So, your config would look like,

  if (environment === 'development') {
    ENV['ember-cli-mirage'] = {
      excludeFilesFromBuild: true

It’s not done ;) Yes, you guys got some bonus too if you are using engines to lazy load assets. Doc-cially, engines are defined as

Engines allow multiple logical applications to be composed together into a single application from the user’s perspective.

Since our codebase is large, we need to modularize and lazy load assets. For that, we prefer in-repo engines. At this point, you would have guessed! Smart! This is question time,

Why we have to worry about the engines file (isolated application) if we are not gonna touch the engine-related modules at all? 🤔🤔🤔

The answer to this question depends on the use-cases and nature of the product/application. In my case, I was free to exclude those files too from the source-map concatenation process as my engines are almost isolated from the rest of the application that to be developed with their own scope. How to exclude engine files?

Ha… First, why the engines files (actually an addon) are included in source-map?

Because we make it so by mentioning it as a developing addon in index.js file of an engine to get the changes reflected in the app simultaneously/instantly for developing purposes.

Yeah, you found the answer, if you actually don’t change the engine files during your development, make those engines as a developed addon 😉 as mentioned below:

let EngineAddon = require('ember-engines/lib/engine-addon');
module.exports = EngineAddon.extend({
  name: 'chatbox',
  isDevelopingAddon() {
    return false;

This is all for today’s flash post 😊 There’s a long way to go 😉 Meet you all in a future post. With respect to the engines, we should come up with configuration settings that will help us to manipulate the engine configuration (both in-repo and standalone engine) during runtime. Comments are welcome on this front. BTW, since the entire blog post is somewhat leaned against test and test cases, I must tell you all that I love test cases as the same level as development process 😇.