Is there a way to count instances from a class?

Question

I need to keep track of how many instances of a class have been created, from within the said class. I need every instance natively to know 'which one' it is.

The only way I could think of was to use global variables but... there may be a better way.

Here is what I want to avoid:

class MyClass {
    this.instanceId = (window.instanceCount == undefined) ? 0 : window.instanceCount + 1;
    window.instanceCount = this.instanceId;
    ...
}

Answer 1

You can statically add a counter to your "class". Here I use a symbol to prevent names collision. Note that I check whether you use Burrito as a function or a class prior to incrementing the counter.

function Burrito() {
  if (this instanceof Burrito) {
    Burrito[Burrito.counterName]++;
  }
}

Burrito.counterName = Symbol();
Burrito[Burrito.counterName] = 0;
Burrito.count = () => Burrito[Burrito.counterName];

new Burrito(); // 1
new Burrito(); // 2
Burrito();     // skipped
new Burrito(); // 3

console.log(Burrito.count());