When or who does pass resolve and reject functions to JS promises?

Question

I have begin learning javascript promises. But I just can\'t understand the concept of promises. The thing that bothers me most is who is passing the Resolver and Reject fun

Answer 1

The Promise constructor is initialized with a callback, and the constructor passes reject and resolve as parameters when the callback is called.

Here is a simple demo:

class PromiseDemo {
  constructor(cb) {
    cb(this.resolve.bind(this), this.reject.bind(this));
  }
  
  resolve(d) {
    console.log('resolve', d);
  }
  
  reject(d) {
    console.log('reject', d);
  }
}

new PromiseDemo((resolve, reject) => {
  Math.random() > 0.5 ? resolve('1') : reject('1');
});