About typescript interface definition

Question

I have a function A which will return function B. The param of function B is object C. C has a property called D whose type is T.

The T is decided when I get B which means I could set T when I call A or some other ways.

So how to define it in typescript? Thanks so much.

I've tried this which will work. But that's not what I want:

interface C<T> {
    d: T;
    e: number;
}

interface B<T> {
    (param: C<T>): void;
}

interface A<T> {
    (): B<T>;
}

const a: A<number> = () => ({d, e}) => {
    console.log(d, e)
};

The things I want maybe something like:

const a: A = () => ({d, e}) => {
    console.log(d, e)
};
const b1 = a<number>();
const b2 = a<string>();

I have no idea about this.

Please provide some code, what have you tried so far?

bugs
– bugs

2020-03-31 14:51:19 +00:00
Commented Mar 31, 2020 at 14:51 — bugs
– bugs, Commented Mar 31, 2020 at 14:51
@bugs Hi. I have appended some code.

PoppinL
– PoppinL

2020-03-31 15:13:54 +00:00
Commented Mar 31, 2020 at 15:13 — PoppinL
– PoppinL, Commented Mar 31, 2020 at 15:13

JeromeBu · Accepted Answer · 2020-03-31 15:50:10Z

2

You are on the right path, I find it cleaner with types rather than interfaces :

interface C<T> {
    d: T;
    e: number;
}

type B<T> = (params: C<T>) => void

type A = <T>() => B<T>

// or inlined : type A = <T>() => (params: C<T>) => void

const a: A = () => ({d, e}) => {
    console.log(d, e)
};

const withNumber = a<number>();
const withString = a<string>();

edited Mar 31, 2020 at 15:50

answered Mar 31, 2020 at 15:18

JeromeBu

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3 Comments

PoppinL Over a year ago

Hi. Thanks for your answer. I forgot the type syntax. Thank you. :) But I wanna set T when I call a. I have no idea about this.

JeromeBu Over a year ago

Right, I just updated my answer to match what you ask

PoppinL Over a year ago

Coooool! Thank you so much! Seems I mix up the generics for interface with pass generics. Really thanks! I'll take a look at that part in typescript again.

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