promises.js

// https://medium.com/@hxu0407/master-these-8-promise-concurrency-control-techniques-to-significantly-improve-performance-5a1c199b6b3c


// 1. Promise.all: Execute in Parallel and Return Results Together
const promise1 = Promise.resolve(1);
const promise2 = Promise.resolve(2);
const promise3 = Promise.resolve(3);
Promise.all([promise1, promise2, promise3])
  .then(results => {
    console.log(results); // Output: [1, 2, 3]
  });
  
  
  
  
// 2. Promise.allSettled: Execute in Parallel and Return All States
const promise1 = Promise.resolve(1);
const promise2 = Promise.reject("Error");
const promise3 = Promise.resolve(3);
Promise.allSettled([promise1, promise2, promise3])
  .then(results => {
    console.log(results);
    /* Output:
    [
      { status: 'fulfilled', value: 1 },
      { status: 'rejected', reason: 'Error' },
      { status: 'fulfilled', value: 3 }
    ]
    */
  })
  
  
  
  
// 3. Promise.race: Execute in Parallel and Return the Fastest
const promise1 = new Promise(resolve => setTimeout(() => resolve("Fast"), 100));
const promise2 = new Promise(resolve => setTimeout(() => resolve("Slow"), 500));
Promise.race([promise1, promise2])
  .then(result => console.log(result)); // Output: "Fast" (whichever resolves first)
  
  
  
  
// 4. Promise.any (ES2021): Execute in Parallel and Return the First Fulfilled
const promise1 = Promise.reject("Error 1");
const promise2 = new Promise(resolve => setTimeout(() => resolve("Success"), 200));
const promise3 = Promise.reject("Error 2");
Promise.any([promise1, promise2, promise3])
  .then(result => console.log(result)) // Output: "Success"
  .catch(error => console.log(error.errors)); // If all reject
  
  
  
  
// 5. Custom Concurrency Control Function: Limit Max Concurrent Requests
async function limitConcurrency(tasks, limit) {
  const results = [];
  const running = new Set();
  
  for (const task of tasks) {
    const promise = task().then(result => {
        running.delete(promise);
        return result;
    });
    running.add(promise);
        results.push(promise);
        if (running.size >= limit) {
          await Promise.race(running);
        }
      }
  return Promise.all(results);