TimeoutCancellation.js

// Given a function fn, an array of arguments args, and a timeout t in milliseconds, 
// return a cancel function cancelFn.

// After a delay of t, fn should be called with args passed as parameters unless 
// cancelFn was invoked before the delay of t milliseconds elapses, specifically 
// at cancelT ms. In that case, fn should never be called.

/**
 * @param {Function} fn
 * @param {Array} args
 * @param {number} t
 * @return {Function}
 */
var cancellable = function(fn, args, t) {
    const timeoutId = setTimeout(function() {
      fn.apply(null, args);
    }, t);
  
    const cancelFn = function() {
      clearTimeout(timeoutId);
    };
  
    return cancelFn;
  };
  
  /**
   *  const result = []
   *
   *  const fn = (x) => x * 5
   *  const args = [2], t = 20, cancelT = 50
   *
   *  const start = performance.now() 
   *
   *  const log = (...argsArr) => {
   *      const diff = Math.floor(performance.now() - start);
   *      result.push({"time": diff, "returned": fn(...argsArr))
   *  }
   *       
   *  const cancel = cancellable(log, args, t);
   *
   *  const maxT = Math.max(t, cancelT)
   *           
   *  setTimeout(() => {
   *     cancel()
   *  }, cancelT)
   *
   *  setTimeout(() => {
   *     console.log(result) // [{"time":20,"returned":10}]
   *  }, maxT + 15)
   */