How do I achieve the class variable functionality in JavaScript?

Question

I want to keep track of how many objects have been created using my constructor function. Currently I'm getting the number by placing a humanCount variable in the global namespace. But, it doesn't look good to me. My code is:

var humanCount = 0;

function Human(name, age){
    this.name = name;
    this.age = age;
    humanCount++;
};

var john = new Human("JOHN", 35);
console.log(humanCount); // prints 1 

var jane = new Human("JANE", 28);
console.log(humanCount);  // prints 2

Any other way to achieve the functionality?

You don't have to use global scope if you don't want to. You can create as many "intermediate" scopes as you like. You can make that value also a property of `Human`. There are lots of possibilities. — Felix Kling, Jan 07 '17 at 07:01
Its not about public/private or scoping issue. Its about creating a variable which will keep track of how many instances are being created. @felixKling — Sajib Biswas, Jan 07 '17 at 07:08
If your question is not about scope or visibility, then what is it about? Can you elaborate on the "it doesn't look good to me" part? What doesn't look and why? — Felix Kling, Jan 07 '17 at 07:10
I am looking for a solution which gives this functionality by attaching a variable to Object/Prototype etc. ( i want to avoid attaching it to global object) Sir. — Sajib Biswas, Jan 07 '17 at 07:15

score 2 · Answer 1 · edited Jan 07 '17 at 07:03

2

You could make the counter a property of the "class" (the constructor):

function Human(name, age){
    this.name = name;
    this.age = age;
    Human.count++;
};

Human.count = 0;

Or you could make it a property of the prototype:

function Human(name, age){
    this.name = name;
    this.age = age;
    Human.prototype.count++;
};

Human.prototype.count = 0;

edited Jan 07 '17 at 07:03

Alexander O'Mara

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answered Jan 07 '17 at 07:01

trincot

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nitishagar · Answer 2 · 2017-01-07T07:07:52.687

1

Create humanCount property like:

function Human(name, age){
    this.name = name;
    this.age = age;
    Human.humanCount = (Human.humanCount || 0) + 1;
};

edited Jan 07 '17 at 07:07

answered Jan 07 '17 at 07:02

nitishagar

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1

*"Create a variable inside the class:"* `humanCount` is a property on the `Human` function, not a variable. – Felix Kling Jan 07 '17 at 07:06
@FelixKling Right – nitishagar Jan 07 '17 at 07:08

How do I achieve the class variable functionality in JavaScript?

2 Answers2