Promises & then/catch

const promise = new Promise((resolve, reject) => {
  if (condition) {
    resolve(value);
  } else {
    reject(error);
  }
});

success and failure
resolve and reject
The Promise executor function takes two parameters: resolve and reject. Important aspects: 1) resolve is called when the Promise successfully completes, 2) reject is called when an error occurs, 3) These functions are provided by the Promise constructor, 4) They can only be called once - subsequent calls are ignored, 5) Calling resolve/reject immediately changes the Promise's state, 6) They can take only one argument (additional arguments are ignored).
then and catch
try and catch