Typescript function annotations

The ways of annotating a function are more than one, and it's a little confusing to pick one to use.

After reading this article, I want to make some conclusion about Typescript annotations.

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TypeScript has a robust inference system, which automatically assigns the best possible data type for values. It works very well for variables, objects, arrays and more, so you do not need to think about writing annotations for them. But for functions, inference evaluates only a return value and assign best possible type candidate for it. That means function arguments are not evaluated, and we need to do it by writing annotations manually.

So, which ways we got to annotate a function?

  1. Annotate a function as `function type`:

    TYPESCRIPT
    const myFunction: (name: string) => void = (name) => console.log(name);

  2. Annotate a function's arguments and its retured value, like how we annotate other variables:

    TYPESCRIPT
    const myFunction = (name: string): void => console.log(name);