How to fix "Unable to determine function entry point" error in TypeScript Azure Functions

What is this article about?

This article explains how to fix the following error when running an Azure Functions app written in TypeScript with the command:

$ func start

Stack: Error: Unable to determine function entry point. If multiple functions are exported, you must indicate the entry point, either by naming it 'run' or 'index', or by naming it explicitly via the 'entryPoint' metadata property.

What is this error?

If the file specified in the scriptFile property of function.json has multiple exports, Azure Functions gets confused about which one to use. Therefore, you need to explicitly define the entry point.

How to fix it

You should explicitly specify the entry point in function.json.

{
  "bindings": [
    {
      "(omitted)": "(omitted)"
    }
  ],
  "scriptFile": "../dist/(function-name)/index.js",
  "entryPoint": "default"
}

Wait, I only have one exported function though?

Unless you intentionally do something otherwise, you'd think that the function exported in index.ts would be the only one.

export default timerTrigger

Even so, this error occurs.

This is because when you build the TS, other exports might be generated in index.js.
For example:

exports.__esModule = true;

So, if you don't explicitly specify it, it results in an error!

Seriously, give me a break!!

This isn't even a function...
In the first place, if there are multiple exports, it should prioritize looking for the one that is export default!
Since both TypeScript and Azure are developed by Microsoft, I really wish they would consider making it a bit more developer-friendly. Please, I'm begging you.