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+---
+title: "JavaScript error \"Super Expression must either be null or a function\""
+date: 2022-04-18T04:05:40-04:00
+draft: true
+toc: false
+images:
+tags:
+  - dev
+  - javascript
+  - typescript
+---
+
+I just got this error when working on some TypeScript code.
+
+```
+Uncaught TypeError: Super Expression must either be null or a function
+```
+
+The line for the error pointed to the constructor of a class. What's happening?
+Circular dependencies it turns out.
+
+```ts
+// in foo.ts
+class Foo {
+  foo() {
+    new Bar().doSomething();
+  }
+}
+
+// in bar.ts
+class Bar extends Foo {
+  // ...
+}
+```
+
+It's obvious when boiled down like this, but it's something you'll want to make
+sure to avoid. I solved this issue by making `Bar` not extend `Foo`. It added
+little to no duplicated code for me in this case, so just separating the classes
+was easy enough.