How do I bring my counter variable inside its function's scope?

Question

var count = 0; 

function goFast(){
    ++count;
    console.log("Go straight and then ");
    var direction = "right"; if (count%2===0){direction="left";}
    turn(direction);
    console.log("Thank you passenger #" + count);
}

var turn = function(direction) {
    console.log("turn to your " + direction)
}

goFast();
goFast();

The goFast function is in charge of counting how many travelers pass through, and asks another function where they should turn (which logs out left or right alternatively).

How can I bring my count variable inside the goFast function and thus better encapsulate it, but without re-initializing it every time the function is invoked of course?

Here is a jsfiddle: http://jsfiddle.net/legolandbridge/sU8T8/

http://stackoverflow.com/questions/5786851/define-global-variable-in-a-javascript-function might help.. — Srinath Mandava, Jun 07 '14 at 20:48
What do you mean "better encapsulate it"? What are you trying to accomplish by "better encapsulating it"? — soktinpk, Jun 07 '14 at 20:50

score 4 · Answer 1 · answered Jun 07 '14 at 20:51

One approach would be to wrap it in a closure and return a function that has access to the count variable. For e.g.

var goFast = (function() {
    var count = 0;
    return function() {
        ++count;
        console.log("Go straight and then ");
        var direction = "right"; if (count%2===0){direction="left";}
        turn(direction);
        console.log("Thank you passenger #" + count);
    };
})();

score 3 · Answer 2 · answered Jun 07 '14 at 20:50

3

Wrap its definition in another function to create a temporary scope.

var goFast = (function() { 
   var count = 0;
   return function() {
       ++count;
       console.log("Go straight and then ");
       var direction = "right"; if (count%2===0){direction="left";}
       turn(direction);
       console.log("Thank you passenger #" + count);
   };
})();

answered Jun 07 '14 at 20:50

DrC

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Thank you, this is exactly what I was looking for. I had seen this technique before but could not reproduce it with this simple example. – collardeau Jun 08 '14 at 11:09

score 0 · Answer 3 · answered Jun 07 '14 at 23:20

You could do something like this, but it's not the prettiest and since turn is not inside goFast() anyways.. yeah don't see the benefit.:

function goFast(){
    if ( !window.count )
            window.count = 0;
    ++count;
    console.log("Go straight and then ");
    var direction = "right"; if (count%2===0){direction="left";}
    turn(direction);
    console.log("Thank you passenger #" + count);
}

var turn = function(direction) {
    console.log("turn to your " + direction)
}

goFast();
goFast();

http://jsfiddle.net/daCrosby/sU8T8/1/

How do I bring my counter variable inside its function's scope?

3 Answers3