Javascript Closure functions

Question

So I'm new to javascript and I am looking for a way to count how many times a function is executed. The code randomly generates a square or circle and displays from the shape is shown to when you click it (reactionTime). That works fine and dandy. But I'm looking for a way to keep track of the number of times a shape is clicked and then eventually the cumulative time to calculate average time per click. If it helps, I come from a pretty good C++ background.

To count number of clicks, I was thinking of adding a closure function. From here: How do I find out how many times a function is called with javascript/jquery?

    myFunction = (function(){
        var count = 0;
        return function(){
            count++
            alert( "I have been called " + count + " times");
        }
     })();

And from here: Function count calls

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

    var ob = increment();

But I tried a global variable and several variations of closure functions to no avail (look for the comments). I tried putting the closure function in other functions. And I also tried something like:

    var increment = makeBox();

I'm wondering if anyone can guide me in the right direction. It would be much appreciated!

    var clickedTime; var createdTime; var reactionTime;

    var clicked; var avg = 0;

    avg = (avg + reactionTime) / clicked;
    document.getElementById("clicked").innerHTML = clicked;
    document.getElementById("avg").innerHTML = avg;

    function getRandomColor() {
    ....
    }

    function makeBox() { // This is the long function that makes box
        createdTime = Date.now();
        var time = Math.random();
        time = time * 3000;

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


        // clicked++; /////////// global variable returns NaN
        // console.log(clicked);
        // alert("Clicked: "+clicked);

        setTimeout(function() {
            if (Math.random() > 0.5) {
                document.getElementById("box").style.borderRadius="75px"; }
            else {
                document.getElementById("box").style.borderRadius="0px"; }

            var top = Math.random(); top = top * 300;
            var left = Math.random(); left = left * 500;

            document.getElementById("box").style.top = top+"px";
            document.getElementById("box").style.left = left+"px";
            document.getElementById("box").style.backgroundColor = getRandomColor();
            document.getElementById("box").style.display = "block";
            createdTime = Date.now();
        }, time);
    }

    ob = increment(); //////////////////////// I think this gives me 1 every time
    alert("Increment: "+ob); //////////////////

    document.getElementById("box").onclick = function() {
        clickedTime = Date.now();
        reactionTime= (clickedTime - createdTime)/1000;
        document.getElementById("time").innerHTML = reactionTime;
        this.style.display = "none";
        makeBox();
    }

    makeBox();

At least the `count++` in the first block is missing a semicolon. — Roope, Aug 23 '15 at 18:32

alaney · Answer 1 · 2015-08-23T19:06:55.650

2

You have a few problems but to answer your question:

You're not defining clicked as a number (or any other type) so trying to perform an operation on undefined returns NaN...because well, it's not a number.
Your second attempt var i = 0; won't work because i is re-defined on each function call.

You should be able to use your gobal variable clicked as long as you set it to zero.

edited Aug 23 '15 at 19:06

answered Aug 23 '15 at 18:45

alaney

613
5
12

Jason Sperske · Accepted Answer · 2015-08-23T19:09:34.293

Here is an example that shows how a closure can count calls to a function:

function add5(y) {
    //A totally normal function
    return y + 5;
}

var counter = 0, /*a counter scoped outside of the function counter function*/
    trackedAdd5 = (function (func) {
        /*This anonymous function is incrementing a counter and then calling the function it is passed*/
        return function () {
            counter++;
            /*The trick is this function returns the output of calling the passed in function (not that it is applying it by passing in the arguments)*/
            return func.apply(this, arguments);
        }
    })(add5); /*calling this tracking function by passing the function to track*/

document.getElementById('run').addEventListener('click', function () {
    /*Here we are treating this new trackedAdd5 as a normal function*/
    var y = document.getElementById('y');
    y.value = trackedAdd5(parseInt(y.value, 10));
    /*Except the outer counter variable now represents the number of times this function has been called*/
    document.getElementById('counter').value = counter;
});

<label> <code>y = </code> 
    <input id='y' value='0' />
    <button id='run'>add5</button>
</label>
<br/>
<label><code>add5()</code> was called
    <input readonly id='counter' value='0' />times</label>

thanks! i'll try that and see what happens. closure functions are confusing — Lewis, Aug 23 '15 at 19:12

score 0 · Answer 3 · answered Aug 23 '15 at 19:13

makeBox.click = 0; // define the function's counter outside the function
makeBox.click++; // replace the `i` usage with this inside the function

About ob = increment();: it is used erroneously (redefines ob many times);

var ob = increment(); // define it once
ob(); // increments the counter

// another way to define `increment`:
var increment = (function () {
    var i = 0;
    return function () {
        return i += 1;
    };
})();

ob = increment(); // ob becomes 1 initially
ob = increment(); // ob becomes 2, etc.

Javascript Closure functions

3 Answers3