leetcode(js): compose() v1 with for loop

export { reduce };

```

### Function Composition (compose())

- [Function Composition on LeetCode](https://leetcode.com/problems/function-composition/description/?envType=study-plan-v2&envId=30-days-of-javascript).

#### for loop

```javascript

/**

 * Applies all functions from left to right. Works as the identity

 * function if `fns` is empty.

 *

 * - T.C: Depends on T.C of input `fns` and `val`.

 * - S.C: Same notes as T.C apply.

 *

 * @param {Array<Function>} fns

 * @returns {(val: unknown) => unknown}

 */

function compose(fns) {

  /**

   * @param {unknown} val

   * @returns {unknown}

   */

  return function composed(val) {

    var lastFnIdx = fns.length - 1,

        result = val,

        i;

    for (i = lastFnIdx; i >= 0; --i)

      result = fns[i](result);

    return result;

  };

}

```

import { compose } from "./compose_v1";

describe("compose()", () => {

  it("is the identity function when fns is empty", () => {

    expect(compose([])(1)).toEqual(1);

  });

  it("composes a single function", () => {

    const add1 = n => n + 1;

    expect(compose([add1])(0)).toEqual(1);

  });

  it("composes from right to left", () => {

    const add1 = n => n + 1;

    const double = n => 2 * n;

    const square = n => n * n;

    //   add1(3) = 4

    // double(4) = 8

    // square(8) = 64

    expect(compose([square, double, add1])(3)).toEqual(64);

    // square(1) = 1

    //   add1(1) = 2

    // double(4) = 4

    expect(compose([square, double, add1])(3)).toEqual(64);

  });

});

/**

 * Applies all functions from left to right. Works as the identity

 * function if `fns` is empty.

 *

 * - T.C: Depends on T.C of input `fns` and `val`.

 * - S.C: Same notes as T.C apply.

 *

 * @param {Array<Function>} fns

 * @returns {(val: unknown) => unknown}

 */

function compose(fns) {

  /**

   * @param {unknown} val

   * @returns {unknown}

   */

  return function composed(val) {

    var lastFnIdx = fns.length - 1,

        result = val,

        i;

    for (i = lastFnIdx; i >= 0; --i)

      result = fns[i](result);

    return result;

  };

}

export { compose };