CODEWITHSUNDEEP
typescript
zacaj
zacaj

Reputation: 2085

Why do Typescript function type signatures include parameter names

New to typescript, so maybe I'm missing something here...

I was trying to write a simple filter function on a container I'd made

class Container<T> {
    filter(predicate: (T) => boolean): Container<T> {
        for(const element of this.contents) {
            if(predicate(element))

and tslint gave me an error about starting variables with capital letters (which is a rule I have on purpose). I wasn't sure what it meant at first, but apparently it's taking the T in (T) => boolean to be the name of the parameter, and not the type. After googling around for some typescript callback examples, I saw everyone typing a function signature as 

(paramName: ParamType) => ReturnType.

But it seems like the paramName here is pointless. I'm not declaring the function here, I'm just giving its signature. Why is this valid Typescript?

Upvotes: 3

Views: 463

Answers (1)

Alexander O&#39;Mara
Alexander O&#39;Mara

Reputation: 60577

The official reason appears to be to "help with readability"

A function’s type has the same two parts: the type of the arguments and the return type. When writing out the whole function type, both parts are required. We write out the parameter types just like a parameter list, giving each parameter a name and a type. This name is just to help with readability. ...

-- TypeScript Handbook - Functions

You are correct that the names are not used.

Upvotes: 3

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