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?

Marcelo Cantos · Accepted Answer · 2011-08-30 12:30:54Z

8

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

var ob = increment();

answered Aug 30, 2011 at 12:30

Marcelo Cantos

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8 Comments

Shef Over a year ago

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

codeandcloud Over a year ago

@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 Over a year ago

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

Marcelo Cantos Over a year ago

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.

Marcelo Cantos Over a year ago

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

|

aljgom · Accepted Answer · 2021-06-21 03:02:57Z

3

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

edited Jun 21, 2021 at 3:02

answered Mar 14, 2017 at 20:53

aljgom

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Comments

paulodiovani · Accepted Answer · 2020-01-15 20:00:17Z

2

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

answered Jan 15, 2020 at 20:00

paulodiovani

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Comments

pldg · Accepted Answer · 2018-11-10 23:46:13Z

1

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/

answered Nov 10, 2018 at 23:46

pldg

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Comments

terrymorse · Accepted Answer · 2020-01-15 21:07:26Z

1

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

answered Jan 15, 2020 at 21:07

terrymorse

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2 Comments

Denis Over a year ago

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

terrymorse Over a year ago

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

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