Function count calls

Question

I'm a beginner with JavaScript so please be patient =)

I am trying to write a function that counts the number of times it is called. What I have so far is a function with a counter that is incremented explicitly:

var increment = function () {
    var i = 0;
    this.inc = function () {i += 1;};
    this.get = function () {return i;};
};

var ob = new increment();
ob.inc();
ob.inc();
alert(ob.get());

But I'm wondering how to call only ob();, so the function could increment calls made to itself automatically. Is this possible and if so, how?

Solution 1

var increment = function() {
    var i = 0;
    return function() { return i += 1; };
};

var ob = increment();

Solution 2

ob = function f(){  
  ++f.count || (f.count = 1);   // initialize or increment a counter in the function object
  return f.count; 
}

Solution 3

A one liner option:

const counter = ((count = 0) => () => count++)()

Usage example:

> counter()
0
> counter()
1
> counter()
2
> counter()
3
> counter()
4
> counter()
5
> counter()
6

Solution 4

Wrap a counter to any function:

/**
 * Wrap a counter to a function
 * Count how many times a function is called
 * @param {Function} fn Function to count
 * @param {Number} count Counter, default to 1
 */
function addCounterToFn(fn, count = 1) {
  return function () {
    fn.apply(null, arguments);
    return count++;
  }
}

See https://jsfiddle.net/n50eszwm/

Solution 5

There are also the new Generator functions, which offer a simple way to write a counter:

function* makeRangeIterator(start = 0, end = 100, step = 1) {
  let iterationCount = 0;
  for (let i = start; i < end; i += step) {
    iterationCount++;
    yield i;
  }
  return iterationCount;
}

const counter = makeRangeIterator();
const nextVal = () => counter.next().value;

console.log("nextVal: ", nextVal()); // 0
console.log("nextVal: ", nextVal()); // 1
console.log("nextVal: ", nextVal()); // 2
console.log("nextVal: ", nextVal()); // 3

View more solutions

Comments

[Shef]

+1. @naveen: The noob seems to be heading that way on his/her own. :)

[naveen]

@Shef: I said its good. Its a while before I realized there were closures. But then js was my secondary language. a tiny perk that has alertboxes :)

[Shef]

@naveen: I just agreed with you. :) I, too, was surprised to see the OP, a self-declared beginner, trying to learn closures.

[Alex S]

The OP's code is almost identical to one of my first attempts to learn JS. Being a noob JS programmer doesn't imply being a noob programmer.

[Admin]

@Marcelo Cantos: dont understand your's laugh cuz that what u wrote isn't increment ... ? Nice work Mr A lot of experience in OP

[Alex S]

@Kamil: Try invoking alert(ob()) a couple of times.

[Vaibhav Pachauri]

@MarceloCantos : I am noon myself :) . I just want to know the reason why do we have to use var ob = increment(); and then call ob(); to increase the 'counter' value. Why does it not increment the counter value if we directly call the increment() function ?

[Alex S]

@Vaibhav: The increment function itself doesn't increment anything. It returns a function that does. ob holds that function.

[Denis]

Hi, how do you re-set this counter to 0?

[terrymorse]

@Denis There is no reset feature, but you can call makeRangeIterator() again to create a new counter.