Reusable function type

Question

I'm trying declare a function type and then use that in a class, and in objects, and interfaces like this:

declare function IUpdateMode(mode: Mode): void;

Then I want to use it like this:

type Foo = {
   updateMode: IUpdateMode
}


class Foo extends React.Component<any> {

    updateRedMode(mode): IUpdateMode {}

}

function updateGreenMode(mode): IUpdateMode {

}

Is this possible in typescript?

Nurbol Alpysbayev · Accepted Answer · 2018-11-10 02:10:46Z

1

I think what you really want is just this:

type UpdateMode = (mode: Mode) => void

Now you can use it anywhere as you mentioned, but with some corrections:

interface IFoo { // interface instead of a type is preferable when possible (e.g. you may extend it)
   updateMode: UpdateMode
}


class Foo extends React.Component<any> implements IFoo {

    updateMode = (mode: Mode) => {}

}

const updateGreenMode: UpdateMode = (mode) => { // there is no way to restrict a classic function to type alias or interface

}

edited Nov 10, 2018 at 2:10

answered Nov 10, 2018 at 1:57

Nurbol Alpysbayev

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3 Comments

Noitidart Over a year ago

Oh thank you! Is it not possible to use this with the function upgradeGreenMod() {} style?

Nurbol Alpysbayev Over a year ago

You are welcome! No, it's not possible unfortunately, to restrict a classic function to some type alias or interface.

Nurbol Alpysbayev Over a year ago

I've polished the answer a bit more. e.g. the (non-mandatory, for-convenience) convention is to add "I" character to the beginning of interfaces, not types. Also class should implement Ifoo interface

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