Hot-patching our dependencies with patch-package


This is also a quick blog post.

Let me tell you the tale of patch-package. Not many people have heard the tale of patch-package. Many prefer to walk the path forked.

Well, the path of patch-package works like this.

About patch-package

Your favourite NPM library has a problem. You need to hot fix it. You send in a PR and it’s stuck in review hell. The poor maintainer is on stress leave and you really don’t want to trouble her/him - they are in Finland, don’t wear shoes, and can’t possibly scale any further.

This is the patch-package path

  1. yarn / npm lock the dependency on that specific version so our entire team and the build pipeline gets the same version

  2. npm install patch-package --save-dev

  3. make changes in node_modules against that library, e.g. “package-banana”

  4. npx patch-package “package-banana” - this creates a folder

  5. add “postinstall": "patch-package" to scripts section in package.json

  6. check in / commit everything. Package.json and /patches/package-banana-*.patch

Now when anyone get latest and run npm install, the build chain will automatically grab that version of the library package-banana and apply your patch.

Then it will build as normal. This works great on Azure DevOps (VSTS) too.

When the library package-banana is finally fixed - update the library version and the patch file won’t work against newer versions.

Bad JavaScript. Expected '(' in our webpack eval chunk

This is a quick blog post for resolving an issue this morning from webpack uglified/minified JavaScript. The error happens in IE and Edge, it simply says:

Expected ‘(‘

This was happening in the middle of a webpack minified chunk so the entire block was wrapped inside eval(““)


  1. Navigate to the end of the webpack chunk, which will tell us the source of this chunk. Scroll past the sourcemap section to the end of the chunk (not the end of the file).

  2. Find the original file that the chunk was created from - now run ESLint over it.
    I didn’t have this handy in the build chain, so I ran it online

  3. The error was spotted as there was a catch{} statement - in plain JavaScript - catch has to collect an argument. So the first syntax is incorrect. It must be the second syntax.

try {
    // do something
catch {
    // incorrect  
try {
    // do something
catch(e) {
    // correct, even if we don't use e  

Modern browsers are more lenient so this error did not appear on all browsers.