To Be Or Not To Be – 2704

🔗LC2704 🟢 Easy 🧩 Pattern – Closures

📅 Day 3/30 Days of JavaScript

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".

Example

Input: func = () => expect(5).toBe(5)
Output: {"value": true}
Explanation: 5 === 5 so this expression returns true.

Input: func = () => expect(5).notToBe(null)
Output: {"value": true}
Explanation: 5 !== null so this expression returns true.

Solution

Here, we need to understand how we are returning an object that has two functions as its properties forming a closure to access the val (argument).

/**
 * @param {string} val
 * @return {Object}
 */
var expect = function (val) {
    return {
        toBe: (value) => {
            if (value === val) {
                return true;
            } else {
                throw new Error("Not Equal");
            }
        },
        notToBe: (value) => {
            if (value !== val) {
                return true;
            } else {
                throw new Error("Equal");
            }
        },
    }
}

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