A setTimeout with delay

Scheduler.js

// Scheduler is setTimeout with an ability to delay
// already scheduled tasks.


// 1. DEFINITION
// -------------
function Scheduler(freq) {  // freq in ms
  this.freq = freq;
  setInterval(this._main.bind(this), this.freq);
}

Scheduler.prototype._main = function() {
  if (this.t) {
    if (this.t === this.freq) {
      this.fn();
    }
    this.t -= this.freq;
  }
};

// Works just like setTimeout.
Scheduler.prototype.assign = function(fn, t) {
  if (t % this.freq !== 0) {
    throw new Error('assign(fn, t): t must be a multiple of freq');
  }
  this.fn = fn;
  this.t = this.max = t;
};

// Delay the task by t (if t < max) or max.
Scheduler.prototype.delay = function(t) {
  if (this.t) {
    this.t = Math.min(this.max, this.t + t);
  }
};


// 2. USAGE
// --------
// Instantiate a scheduler that runs things every second.
var s = new Scheduler(1000);

// Schedule 'hi' to be displayed in 5 seconds.
s.assign(function() {console.log('hi');}, 5000);

// Suppose 1 second remained for 'hi' to be displayed;
// now it will display in 3 seconds (unless delayed again).
s.delay(2000);

// Note that you can keep delaying a task, but it will always be
// bounded by the originally scheduled time (here, 5 seconds).

Scheduler.ts

// Scheduler in TypeScript

export class Scheduler {
  fn: Function;  // function to call when time comes
  freq: number;  // in ms
  t_orig: number;  // original time scheduled
  t: number;  // time scheduled

  constructor(freq: number) {
    this.freq = freq;
    setInterval(this._loop.bind(this), this.freq);
  }

  _loop() {
    if (this.t) {
      if (this.t === this.freq) {
        this.fn();
      }
      this.t -= this.freq;
    }
  }

  // Works just like setTimeout.
  assign(fn: Function, t: number) {
    if (t % this.freq !== 0) {
      throw new Error('assign(fn, t): t must be a multiple of freq');
    }
    this.fn = fn;
    this.t = this.t_orig = t;
  }

  // Delay the task by t (if t < t_orig) or t_orig.
  delay(t: number) {
    if (this.t) {
      this.t = Math.min(this.t_orig, this.t + t);
    }
  }
}

Scheduler_use.ts

import { Scheduler } from "./scheduler";


// Instantiate a scheduler that runs things every second.
var s = new Scheduler(1000);

// Schedule 'hi' to be displayed in 5 seconds.
s.assign(() => console.log('hi'), 5000);

// Suppose 1 second remained for 'hi' to be displayed;
// now it will display in 3 seconds (unless delayed again).
s.delay(2000);

// Note that you can keep delaying a task, but it will always be
// bounded by the originally scheduled time (here, 5 seconds).