A pipe function, similar to compose function, in TypeScript.

pipe.ts

/**
 * Since TypeScript doesn't support **Variadic Kinds** we explicitly have to
 * define the type of all the possible usages as method overloads.
 *
 * https://github.com/microsoft/TypeScript/issues/5453
 *
 * Our `pipe` supports N arguments, but we probably will not use more than 10.
 */
// prettier-ignore
type Pipe = {
  <Args extends any[], T0>(fn0: (...xs: Args) => T0): (...xs: Args) => T0;
  <Args extends any[], T0, T1>(fn0: (...xs: Args) => T0, fn1: (x: T0) => T1): (...xs: Args) => T0;
  <Args extends any[], T0, T1, T2>(fn0: (...xs: Args) => T0, fn1: (x: T0) => T1, fn2: (x: T1) => T2): (...xs: Args) => T2;
  <Args extends any[], T0, T1, T2, T3>(fn0: (...xs: Args) => T0, fn1: (x: T0) => T1, fn2: (x: T1) => T2, fn3: (x: T2) => T3): (...xs: Args) => T3;
  <Args extends any[], T0, T1, T2, T3, T4>(fn0: (...xs: Args) => T0, fn1: (x: T0) => T1, fn2: (x: T1) => T2, fn3: (x: T2) => T3, fn4: (x: T3) => T4): (...xs: Args) => T4;
  <Args extends any[], T0, T1, T2, T3, T4, T5>(fn0: (...xs: Args) => T0, fn1: (x: T0) => T1, fn2: (x: T1) => T2, fn3: (x: T2) => T3, fn4: (x: T3) => T4, fn5: (x: T4) => T5): (...xs: Args) => T5;
  <Args extends any[], T0, T1, T2, T3, T4, T5, T6>(fn0: (...xs: Args) => T0, fn1: (x: T0) => T1, fn2: (x: T1) => T2, fn3: (x: T2) => T3, fn4: (x: T3) => T4, fn5: (x: T4) => T5, fn6: (x: T5) => T6): (...xs: Args) => T6;
  <Args extends any[], T0, T1, T2, T3, T4, T5, T6, T7>(fn0: (...xs: Args) => T0, fn1: (x: T0) => T1, fn2: (x: T1) => T2, fn3: (x: T2) => T3, fn4: (x: T3) => T4, fn5: (x: T4) => T5, fn6: (x: T5) => T6, fn7: (x: T6) => T7): (...xs: Args) => T7;
  <Args extends any[], T0, T1, T2, T3, T4, T5, T6, T7, T8>(fn0: (...xs: Args) => T0, fn1: (x: T0) => T1, fn2: (x: T1) => T2, fn3: (x: T2) => T3, fn4: (x: T3) => T4, fn5: (x: T4) => T5, fn6: (x: T5) => T6, fn7: (x: T6) => T7, fn8: (x: T7) => T8): (...xs: Args) => T8;
  <Args extends any[], T0, T1, T2, T3, T4, T5, T6, T7, T8, T9>(fn0: (...xs: Args) => T0, fn1: (x: T0) => T1, fn2: (x: T1) => T2, fn3: (x: T2) => T3, fn4: (x: T3) => T4, fn5: (x: T4) => T5, fn6: (x: T5) => T6, fn7: (x: T6) => T7, fn8: (x: T7) => T8, fn9: (x: T8) => T9): (...xs: Args) => T9;
}

/**
 * Performs function composition in LTR (Left To Right) direction.
 * @example
 * const normalizeWhiteSpaces = text => name.replace(/\s+/g, ' ').trim();
 *
 * const getInitials = pipe(
 *   normalizeWhiteSpaces,
 *   name => name.split(' ').map(name => name.charAt(0)),
 *   initials => initials.join('').toLocaleUpperCase()
 * );
 *
 * getInitials('Vitor Luiz Cavalcanti');
 * //=> "VLC"
 * @param fn0 - An arity N function. Its result is the argument of next one.
 * @param fns - Functions of arity 1. Each one's result is next's argument.
 */
const pipe: Pipe = (
  fn0: (...xs: any[]) => any,
  ...fns: ((x: any) => any)[]
) => (...args: any[]) => fns.reduce((x, fn) => fn(x), fn0(...args));

export default pipe;