What is not assignable to parameter of type never error in TypeScript

Question

This is my code:

const foo = (foo: string) => {
  const result = []
  result.push(foo)
}

I get the following TS error:

[ts] Argument of type 'string' is not assignable to parameter of type 'never'.

What exactly am I doing wrong?

Answer 1

All you have to do is define your result as a string array, like this:

const result : string[] = [];

Without defining the array type, by default, it will be never. So when you tried to add a string to it, it was a type mismatch, and so it threw the error you saw.