Typescript - Higher order function types

Question

I'm getting really excited about TypeScript. How do you set the type of a function parameter?

function twoMoreThanYou(calculateANumber: Function):number {
    return calculateANumber(4) + 2;
}

function double(n:number):number {
    return n*2;
}

console.log("TWO MORE", twoMoreThanYou(double))

How can I type calculateANumber better? I'd like to specify that it must be a function that takes a number and returns a number.

Can I then make an "interface" or some shorthand for that type so I can make my higher order function signatures more readable?

mixture · Accepted Answer · 2014-08-06 20:37:56Z

37

These both work

interface NumberFunction extends Function {
    (n:number):number;
}

function twoMoreThanYou(calculateANumber: (n:number)=>number):number {
    ...
}

function twoMoreThanYou(calculateANumber: NumberFunction):number {
    ...
}

edited Aug 6, 2014 at 20:37

mixture

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answered Nov 6, 2012 at 0:34

Sean Clark Hess

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1 Comment

asawyer Over a year ago

You don't have to specify the return type for the twoMoreThanYou function with the NumberFunction interface. Type inference!

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