const promises = [];

if(true) {
   const promise1 = fetch('https://jsonplaceholder.typicode.com/posts/1').then(res => ({ res: res, promise: 'promise1' }));
   promises.push(promise1);
}

if(false) {
   const promise2 = fetch('https://jsonplaceholder.typicode.com/posts/2').then(res => ({ res: res, promise: 'promise2' }));
   promises.push(promise2);
}

Promise.all(promises).then(res => console.log(res));
 Run code snippet