Using JS Promise as an interrupt

Question

I wanted to directly call a function (like interrupt handler) when a certain condition is met. I didn't want to using "polling" for that as it increases time complexity.

count = 1
p = new Promise((resolve, reject)=>{
    
    if(count == 2){
        resolve("hello")
    }
});

p.then((msg)=>{
    console.log(msg)
})

console.log("1 now");
count = 2;

I expected console.log(msg) to run when count=2 but this is not the case. It turned out that the promise is still "pending". What is the reason this happens? And how do I implement my question.

Answer 1

Proxy is one of the solutions for this. But I post another approach for your case.

You can define a custom class or object, and work with that class. Also you register your custom listener for it, and do whatever.

This is a sample of my code. Maybe it will give you some ideas for your solution.

class MyObject {
  constructor(value, func) {
    this._value = value;
    this._listener = func;
  }

  get value() {
    return this._value;
  }

  set value(newValue) {
    this._listener(newValue);
    this._value = newValue;
  }
}

function customListener(changedValue) {
  console.log(`New Value Detected: ${changedValue}`);
}

const count = new MyObject(1, customListener);

count.value = 2;