Exploring the concepts of Function Type and Function Interface within Typescript

Is it possible to create a function interface in typescript that mirrors the parameters and return type of a function?

For example, when we have a function like

meth (a : {b: B, c: C}) : {b: B, c: C} {...}

we can define an interface A as follows:

interface A {
    b : B;
    c : C;
}
meth (a : A) : A {...}

However, what about cases where the function has a different signature, like

meth (a : (b: B) => C) : (b: B) => C {...}

Is there a way to define a function type similarly so that we can write

meth (a : A) : A {...}

once again?

Answer №1

When working with interfaces, it's essential to understand call signatures. The syntax used is actually a more concise version of the full, verbose syntax:

interface A 
{
    (b: B) : C
}
function meth (a : A) : A { return a; }

One advantage of the interface syntax is its ability to support multiple overloads for a function:

interface A {
    (b: B): D
    (d: D, b: B): C
}
function meth(a: A) : void
{
    a(new B()); // Call overload with one argument
    a(new D(), new B()); // Call overload with two arguments 
}

meth((b: B | D, d?: D|B) => new D());

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