decojs.js

/** A "decorator" -- a function that:
 *    - takes a function as its arg
 *    - returns a "wrapped version" of that function
 *
 * In this case: the wrapped version runs the real function,
 * but keeps track of how long it took to run.
 */

function timeit(fn) {
  function wrapper(...args) {
    const startTime = Date.now();
    const result = fn(...args);
    const timeInMsec = Date.now() - startTime;
    console.debug(fn.name, `(${timeInMsec} ms)`, args, result);
    return result;
  }

  return wrapper;
}


/** An example of a function we'd like to profile: to make it slow, give
 it a big `n` and a tiny `chance`  */

let slowishThing = function (n, chance) {
  for (let i = 0; i < n; i++) {
    if (Math.random() < chance) return true;
  }
  return false;
};

/** A "wrapped" version of our function: we'll just reassign it to the same
 * name --- now when you call this function, it will run timeit wrapped
 * function, which ultimately calls the real slowishThing */

slowishThing = timeit(slowishThing);



console.log(slowishThing(10000000, 0.000000001));