How to decrease prod bundle size?

Question

I have a simple app, initialized by angular-cli.

It display some pages relative to 3 routes. I have 3 components. On one of this page I use lodash and Angular 2 HTTP modules to get some data (using RxJS Observables, map and subscribe). I display these elements using a simple *ngFor.

But, despite the fact my app is really simple, I get a huge (in my opinion) bundle package and maps. I don't talk about gzip versions though but size before gzipping. This question is just a general recommendations inquiry.

Some tests results:

ng build

Hash: 8efac7d6208adb8641c1 Time: 10129ms chunk {0} main.bundle.js, main.bundle.map (main) 18.7 kB {3} [initial] [rendered]

chunk {1} styles.bundle.css, styles.bundle.map, styles.bundle.map (styles) 155 kB {4} [initial] [rendered]

chunk {2} scripts.bundle.js, scripts.bundle.map (scripts) 128 kB {4} [initial] [rendered]

chunk {3} vendor.bundle.js, vendor.bundle.map (vendor) 3.96 MB [initial] [rendered]

chunk {4} inline.bundle.js, inline.bundle.map (inline) 0 bytes [entry] [rendered]

Wait: 10Mb vendor bundle package for such a simple app?

ng build --prod

Hash: 09a5f095e33b2980e7cc Time: 23455ms chunk {0} main.6273b0f04a07a1c2ad6c.bundle.js, main.6273b0f04a07a1c2ad6c.bundle.map (main) 18.3 kB {3} [initial] [rendered]

chunk {1} styles.bfdaa4d8a4eb2d0cb019.bundle.css, styles.bfdaa4d8a4eb2d0cb019.bundle.map, styles.bfdaa4d8a4eb2d0cb019.bundle.map (styles) 154 kB {4} [initial] [rendered]

chunk {2} scripts.c5b720a078e5464ec211.bundle.js, scripts.c5b720a078e5464ec211.bundle.map (scripts) 128 kB {4} [initial] [rendered]

chunk {3} vendor.07af2467307e17d85438.bundle.js, vendor.07af2467307e17d85438.bundle.map (vendor) 3.96 MB [initial] [rendered]

chunk {4} inline.a345391d459797f81820.bundle.js, inline.a345391d459797f81820.bundle.map (inline) 0 bytes [entry] [rendered]

Wait again: such a similar vendor bundle size for prod?

ng build --prod --aot

Hash: 517e4425ff872bbe3e5b Time: 22856ms chunk {0} main.95eadabace554e3c2b43.bundle.js, main.95eadabace554e3c2b43.bundle.map (main) 130 kB {3} [initial] [rendered]

chunk {1} styles.e53a388ae1dd2b7f5434.bundle.css, styles.e53a388ae1dd2b7f5434.bundle.map, styles.e53a388ae1dd2b7f5434.bundle.map (styles) 154 kB {4} [initial] [rendered]

chunk {2} scripts.e5c2c90547f3168a7564.bundle.js, scripts.e5c2c90547f3168a7564.bundle.map (scripts) 128 kB {4} [initial] [rendered]

chunk {3} vendor.41a6c1f57136df286f14.bundle.js, vendor.41a6c1f57136df286f14.bundle.map (vendor) 2.75 MB [initial] [rendered]

chunk {4} inline.97c0403c57a46c6a7920.bundle.js, inline.97c0403c57a46c6a7920.bundle.map (inline) 0 bytes [entry] [rendered]

ng build --aot

Hash: 040cc91df4df5ffc3c3f Time: 11011ms chunk {0} main.bundle.js, main.bundle.map (main) 130 kB {3} [initial] [rendered]

chunk {1} styles.bundle.css, styles.bundle.map, styles.bundle.map (styles) 155 kB {4} [initial] [rendered]

chunk {2} scripts.bundle.js, scripts.bundle.map (scripts) 128 kB {4} [initial] [rendered]

chunk {3} vendor.bundle.js, vendor.bundle.map (vendor) 2.75 MB [initial] [rendered]

chunk {4} inline.bundle.js, inline.bundle.map (inline) 0 bytes [entry] [rendered]

So a few questions for deploying my app on prod:

• Why are the vendor bundles so huge?
• Is tree shaking properly used by angular-cli?
• How to improve this bundle size?
• Are the .map files required?
• Are the testing features included in bundles? I don't need them in prod.
• Generic question: what are the recommanded tools to pack for prod? Maybe angular-cli (using Webpack in the background) is not the best option? Can we do better?

I searched many discussions on Stack Overflow, but I haven't found any generic question.

Answer 1

Update February 2020

Since this answer got a lot of traction, I thought it would be best to update it with newer Angular optimizations:

1. As another answerer said, ng build --prod --build-optimizer is a good option for people using less than Angular v5. For newer versions, this is done by default with ng build --prod
2. Another option is to use module chunking/lazy loading to better split your application into smaller chunks
3. Ivy rendering engine comes by default in Angular 9, it offers better bundle sizes
4. Make sure your 3rd party deps are tree shakeable. If you're not using Rxjs v6 yet, you should be.
5. If all else fails, use a tool like webpack-bundle-analyzer to see what is causing bloat in your modules
6. Check if you files are gzipped

---

Some claims that using AOT compilation can reduce the vendor bundle size to 250kb. However, in BlackHoleGalaxy's example, he uses AOT compilation and is still left with a vendor bundle size of 2.75MB with ng build --prod --aot, 10x larger than the supposed 250kb. This is not out of the norm for angular2 applications, even if you are using v4.0. 2.75MB is still too large for anyone who really cares about performance, especially on a mobile device.

There are a few things you can do to help the performance of your application:

1) AOT & Tree Shaking (angular-cli does this out of the box). With Angular 9 AOT is by default on prod and dev environment.

2) Using Angular Universal A.K.A. server-side rendering (not in cli)

3) Web Workers (again, not in cli, but a very requested feature)
see: https://github.com/angular/angular-cli/issues/2305

4) Service Workers
see: https://github.com/angular/angular-cli/issues/4006

You may not need all of these in a single application, but these are some of the options that are currently present for optimizing Angular performance. I believe/hope Google is aware of the out of the box shortcomings in terms of performance and plans to improve this in the future.

Here is a reference that talks more in depth about some of the concepts i mentioned above:

https://medium.com/@areai51/the-4-stages-of-perf-tuning-for-your-angular2-app-922ce5c1b294