2723-AddTwoPromises.js

// 2723. 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.
 
// Constraints:
//         promise1 and promise2 are promises that resolve with a number

/**
 * @param {Promise} promise1
 * @param {Promise} promise2
 * @return {Promise}
 */
var addTwoPromises = async function(promise1, promise2) {
    // solution 1
    return await promise1 + await promise2

    // solution 2
    // return await Promise.all([promise1, promise2]).then(([a, b]) => a + b)

    // solution 3
    // const [a, b] = await Promise.all([promise1, promise2])
    // return a + b

    // solution 4
    // return new Promise((resolve, reject) => {
    //     Promise.all([promise1, promise2]).then(([a, b]) => {
    //         resolve(a + b)
    //     }).catch(reject)
    // })
};

var addTwoPromises1 = async function(promise1, promise2) {
    return await Promise.all([promise1, promise2]).then(([a, b]) => a + b)
};

var addTwoPromises2 = async function(promise1, promise2) {
    const [a, b] = await Promise.all([promise1, promise2])
    return a + b
};

var addTwoPromises3 = async function(promise1, promise2) {
    return new Promise((resolve, reject) => {
        Promise.all([promise1, promise2]).then(([a, b]) => {
            resolve(a + b)
        }).catch(reject)
    })
};

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

addTwoPromises(Promise.resolve(2), Promise.resolve(2))
.then(console.log); // 4
addTwoPromises1(Promise.resolve(2), Promise.resolve(2))
.then(console.log); // 4
addTwoPromises2(Promise.resolve(2), Promise.resolve(2))
.then(console.log); // 4
addTwoPromises3(Promise.resolve(2), Promise.resolve(2))
.then(console.log); // 4