Dealing with ReferenceError can't access lexical declaration before initialization issues in an Angular application

Posted on: 2022-10-20 17:11:59

So, there you are, minding your own business when you start getting an error that looks like this:

ERROR Error: Uncaught (in promise): ReferenceError: can't access lexical declaration 'NewState' before initialization NewState@http://localhost:8100/default-src_app_modules_messaging_messaging-components_messaging-components_module_ts-src_app_pages-f15b60.js:248:64 

If you search for this error, you'll find lots of links to the MDN article on ReferenceError but this isn't helpful. Beacuse at this point you've got TypeScript + Webpack mangling your output so badly that you have absolutely no idea what's going on.

Well, here's the thing, Angular & Webpack do a pretty good job of making sure that you're not hoisting things out of order or doing weird things with your dependency. Here's your real problem:

You've got a circular dependency

But wait, doesn't Angular already check for circular dependencies? Yeah. Obvious ones, they sure do. You can't have an NgModule that references another NgModule which references back to the other NgModule. It would detect that and throw an error.

Here's an example:,two.module.ts

It doesn't even compile. It just stack overflows.

I tried to reproduce the actual issue we had in StackBlitz... it didn't work.

The truth is, some circular references are just not detected without a bit of extra work.

Angular CLI to the rescue: ng build --show-circular-dependencies

Warning: Circular dependency detected:
src/app/modules/chat/state/conversations/small-conversation.state.ts -> 
src/app/pages/trainer-messages/ -> 

This revealed our state model was dependent upon a page... that depends on our state model...? What?

It was an enum

Ultimately, we had an enum in that page's file and that file depended upon the state model itself. Moving that enum to a new file and including it on both pages fixed the issue.

Here's hoping this page helps other people!