compose

Performs right-to-left function composition.

Use Array.prototype.reduce() to perform right-to-left function composition. The last (rightmost) function can accept one or more arguments; the remaining functions must be unary.

typescript

const compose = (...fns: Func<any>[]) =>
  fns.reduce(
    (f, g) =>
      (...args: any[]) =>
        f(...castArray(g(...args)))
  );

You can have look on implementation of [castArray]

typescript

const add5 = (x: number) => x + 5;
const multiply = (x: number, y: number) => x * y;
const multiplyAndAdd5 = compose(add5, multiply);
multiplyAndAdd5(5, 2); // 15

Complex Example- Return with tuple:

typescript

const multiply = (x: number, y: number) => x * y; // 5* 2 = 10
const add3 = (x: number) => [x + 3, 3]; // [10+3, 3] = [13, 3]
const add = (x: number, y: number) => x + y; // 13 + 3 = 16
const multiplyAndAdd3 = compose(add, add3, multiply);
assertEquals(multiplyAndAdd3(5, 2), 16);