What could be the reason for my function throwing a TypeError with the message "<function> is not a function"?

Every time I try to call a function that clearly appears to be defined as a function, I continuously receive the error message: TypeError: [function name] is not a function.

To demonstrate the issue, here is a simple example:

main.ts

import someFunction from './someFunction'
export const baseUrl = document.location.protocol + '//' + document.location.hostname

someFunction(); //causing TypeError: someFunction is not a function

someFunction.ts

import {Foo} from './Foo'
export default function someFunction(): void {
    //some code here
    let foo = new Foo();
    //some other code here
}

Foo.ts

import {baseUrl} from './main'
export class Foo{
    constructor()

    private someRandomPrivateFunction(): void {
        //some code
        let url = baseUrl + "other/stuff"; //removing this line fixes the TypeError
        //some other code
    }
}

Further information on the tools and versions in use:

Typescript version 1.8 is being used, targeting ES5, and generating modules using AMD.

RequireJS version 2.2.0 is implemented and data-main points to main.

The testing environment was Chrome version 52.0.2743.116 m.

Answer №1

It took me an unreasonable amount of time to unravel this issue, only to discover that it all came down to a circular reference.

In Foo.ts, removing the reference to baseUrl resolved everything smoothly since baseUrl is a dependency from main.ts

The solution was simple - move baseUrl to a separate file named baseUrl.ts

This experience taught me some valuable lessons:

  1. Avoid dependencies on main.ts... that should have been evident from the start.
  2. Circular references can result in confusing error messages, seemingly unrelated and buried deep within layers of code. Relying solely on error messages to identify circular dependencies is not reliable.

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