30 Days of Javascript 12 - Add Two Promises

Given two promises promise1 and promise2, return a new promise. promise1 and promise2 will both resolve with a number. The returned promise should resolve with the sum of the two numbers.

Example 1:

Input: promise1 = new Promise(resolve => setTimeout(() => resolve(2), 20)), promise2 = new Promise(resolve => setTimeout(() => resolve(5), 60)) Output: 7 Explanation: The two input promises resolve with the values of 2 and 5 respectively. The returned promise should resolve with a value of 2 + 5 = 7. The time the returned promise resolves is not judged for this problem. Example 2:

Input: promise1 = new Promise(resolve => setTimeout(() => resolve(10), 50)), promise2 = new Promise(resolve => setTimeout(() => resolve(-12), 30)) Output: -2 Explanation: The two input promises resolve with the values of 10 and -12 respectively. The returned promise should resolve with a value of 10 + -12 = -2.

/**
 * @param {Promise} promise1
 * @param {Promise} promise2
 * @return {Promise}
 */
var addTwoPromises = async function (promise1, promise2) {
  const p1 = await promise1;
  const p2 = await promise2;
  return p1 + p2;
};

/**
 * addTwoPromises(Promise.resolve(2), Promise.resolve(2))
 *   .then(console.log); // 4
 */

Inside the function, it uses the await keyword to wait for each promise to resolve and assigns their resolved values to p1 and p2, respectively.

Then, it performs the addition of p1 and p2 using the + operator. The + operator is used here to concatenate the values if they are strings or perform numeric addition if they are numbers.