CODEWITHSUNDEEP
functiontypescriptparametersvariable-types
user1675891
user1675891

Reputation:

What is the variable type if it takes a function?

I'm writing a constructor that takes a string, and int and a function (and possibly something more that I'm not aware of at the moment). This far, I've got the following.

export class Blobb {
  constructor(public value: number, 
              public name: string, 
              public mapping: function,
              public misc: any) { ... }
}

Apparently, the variable mapping crashes the transpilation because function isn't a valid type. I'm not sure what to do with it.

Is there a specific type for a function being passed to the constructor? Is any the preferred approach? Should I consider declaring my own type?

If it's of any significance, the function to be passed will always be something like this (but with varying computations, of course).

mapping() {
  this.value * 13 + ": " + this.name;
}

Upvotes: 0

Views: 127

Answers (4)

Saravana
Saravana

Reputation: 40642

You can annotate the parameter with the exact function signature instead of specifying it just as a Function. In your case it can be typed as () => void:

export class Blobb {
  constructor(public value: number, 
              public name: string, 
              public mapping: () => void,
              public misc: any) { ... }
}

TypeScript function types: https://www.typescriptlang.org/docs/handbook/functions.html#function-types

Upvotes: 2

Kenneth Chau
Kenneth Chau

Reputation: 31

I think you need Function with an uppercase 'F' instead of function.

function is the key word to declare a new function I believe.

Upvotes: 0

CharithW
CharithW

Reputation: 61

You could use the interface 'Function' in es2015 or above, so it could look like,

export class Blobb {
  constructor(public value: number, 
              public name: string, 
              public mapping: Function,
              public misc: any) { ... }
}

Upvotes: 0

Nico Van Belle
Nico Van Belle

Reputation: 5156

I have not used them myself but from the documents, I see that Type Aliases are a thing (Introduced in TS 1.4);

e.g.: 

type NameResolver = () => string;
function getName(n: NameOrResolver): Name {...}

Typescript Advanced Types

Upvotes: 1

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