Timeout change args without re setTimeout - node.js

Question

const timer = setTimeout(({a, b}) => {
console.log(a + b)
}, 3000, {a:1, b:2});
setTimeout(() => {
Object.assign(timer._timerArgs,[{a:2, b:2}])
}, 1000)
// Output: 4
Please have a look at this. What I'm going to do is, going to change the timer args if needed before it's called.
I don't want to use clearTimeout and setTimeout again for this process.
But not sure this is the right way. And plus how can I set the priority per each timer in case the timeout will be the same.

Answer 1

I don't know where you got ._timerArgs from. I've never seen that. Without dipping into undocumented properties (that are only present in node.js), you can do it like this:
const objA = {a:1, b:2};
const timer = setTimeout(({a, b}) => {
console.log(a + b);
}, 500, objA);
objA.a = 2;
objA.b = 3;
This will output 5 which reflects that you changed the property values before the timer callback fired.
Since objects in Javascript are passed by pointer (not copied), you can still modify the object that objA points at any time before the timer fires and see the effect inside the timer callback.
But, then you don't even have to pass the arguments into the setTimeout(). You can just reference a parent scoped variable in the callback:
const objA = {a:1, b:2};
const timer = setTimeout(() => {
console.log(objA.a + objA.b);
}, 500);
objA.a = 2;
objA.b = 3;
This will also output 5.
If you want arbitrary argument modification (not properties embedded in an object), and you want it to be only using supported, standard tools that work in all implementations of Javascript, then you can't do that with just setTimeout(). You could make your own timer wrapper though:
class MyTimer {
constructor(fn, t, ...args) {
this.args = args;
this.fired = false;
this.timer = setTimeout(() => {
this.fired = true;
fn.apply(null, this.args);
}, t);
}
cancel() {
clearTimeout(this.timer);
}
hasFired() {
return this.fired;
}
}
const timer = new MyTimer((...args) => {
console.log("timer callback arguments:", args);
}, 500, "hello", "goodbye");
timer.args = ["ola", "adios", "amor", "amigo"];
You can then modify the array in the .args property at any time before the timer fires and they will be passed to the timer callback.