概要

30 Days of JavaScript でJavaScriptの基礎を学ぶためのプランをやってみる。

進捗

2667. Create Hello World Function

Write a function createHelloWorld. It should return a new function that always returns “Hello World”.

function createHelloWorld() {
  return function (...args) {
    return "Hello World";
  };
}

// Example 1
const f1 = createHelloWorld();
console.log(f1()); // Output: "Hello World"

// Example 2
const f2 = createHelloWorld();
console.log(f2({}, null, 42)); // Output: "Hello World"

2620. Counter

Given an integer n, return a counter function. This counter function initially returns n and then returns 1 more than the previous value every subsequent time it is called (n, n + 1, n + 2, etc).

/**
 * @param {number} n
 * @return {Function} counter
 */
var createCounter = function (n) {
  return function () {
    return n++;
  };
};

/**
 * const counter = createCounter(10)
 * counter() // 10
 * counter() // 11
 * counter() // 12
 */

/**
 * @param {string} val
 * @return {Object}
 */
var expect = function (val) {
  return {
    /**
     * toBe(val) accepts another value and returns true
     * if the two values === each other. If they are not equal,
     * it should throw an error "Not Equal".
     * @param expected
     */
    toBe: function (expected) {
      if (val !== expected) {
        throw new Error("Not Equal");
      }

      return true;
    },
    /**
     * notToBe(val) accepts another value and returns true
     * if the two values !== each other. If they are equal,
     * it should throw an error "Equal".
     */
    notToBe: function (expected) {
      if (val === expected) {
        throw new Error("Equal");
      }

      return true;
    },
  };
};
/**
 * expect(5).toBe(5); // true
 * expect(5).notToBe(5); // throws "Equal"
 */

2704. To Be Or Not To Be

Write a function expect that helps developers test their code. It should take in any value val and return an object with the following two functions.

toBe(val) accepts another value and returns true if the two values === each other. If they are not equal, it should throw an error “Not Equal”. notToBe(val) accepts another value and returns true if the two values !== each other. If they are equal, it should throw an error “Equal”.

/**
 * @param {string} val
 * @return {Object}
 */
var expect = function (val) {
  return {
    /**
     * toBe(val) accepts another value and returns true
     * if the two values === each other. If they are not equal,
     * it should throw an error "Not Equal".
     * @param expected
     */
    toBe: function (expected) {
      if (val !== expected) {
        throw new Error("Not Equal");
      }

      return true;
    },
    /**
     * notToBe(val) accepts another value and returns true
     * if the two values !== each other. If they are equal,
     * it should throw an error "Equal".
     */
    notToBe: function (expected) {
      if (val === expected) {
        throw new Error("Equal");
      }

      return true;
    },
  };
};
/**
 * expect(5).toBe(5); // true
 * expect(5).notToBe(5); // throws "Equal"
 */