Get all instances of class in Javascript

Question

I thought there would already be an answer for this but I can\'t seem to find one.. How can I run a particular class method on all instances of this class in Javascript?

Answer 1

You can create a static array and store it on your constructor function:

MyClass.allInstances = [];
MyClass.allInstances.push(this);

However, you need some way to figure out when to remove instances from this array, or you'll leak memory.

Answer 2

You'll need to store a list of instances yourself:

function someClass(param) {

  // add to all
  if (this.constructor.all === undefined) {
    this.constructor.all = [this];
  } else {
    this.constructor.all.push(this);
  }

  // set param
  this.logParam = function() { console.log(param); };
}

var instance1 = new someClass(1);
var instance2 = new someClass(2);

for (var i = 0; i < someClass.all.length; i++) {
  someClass.all[i].logParam();
}

If memory leaks are a concern then you can create a method for deleting instances when you are done with them:

function someClass(param) {

  ...

  this.destroy = function() {
    var all = this.constructor.all;
    if (all.indexOf(this) !== -1) {
      all.splice(all.indexOf(this), 1);
    }
    delete this;
  }
}

Answer 3

You'll have to provide a custom implementation.

I would do something like this :

function Class() {
    Class.instances.push(this);
};
Class.prototype.destroy = function () {
    var i = 0;
    while (Class.instances[i] !== this) { i++; }
    Class.instances.splice(i, 1);
};
Class.instances = [];

var c = new Class();
Class.instances.length; // 1
c.destroy();
Class.instances.length; // 0

Or like this :

function Class() {};
Class.instances = [];
Class.create = function () {
    var inst = new this();
    this.instances.push(inst);
    return inst;
};
Class.destroy = function (inst) {
    var i = 0;
    while (Class.instances[i] !== inst) { i++; }
    Class.instances.splice(i, 1);
};

var c = Class.create();
Class.instances.length; // 1
Class.destroy(c);
Class.instances.length; // 0

Then you could loop through all instances like so :

Class.each = function (fn) {
    var i = 0, 
        l = this.instances.length;
    for (; i < l; i++) {
        if (fn(this.instances[i], i) === false) { break; }
    }
};

Class.each(function (instance, i) {
    // do something with this instance
    // return false to break the loop
});

Answer 4

Sorry for such a late reply, but I found myself trying to achieve this and I think this may be a simpler answer.

Say you want all instances of class MyClass, only get instances created at top window level (not including instances created inside a closure):

for (var member in window)
{
    if (window[member] instanceof MyClass)
        console.info(member + " is instance of MyClass");
}

Answer 5

In Chrome 62+ you can use queryObjects which will not work in native JavaScript code but in the console so it's great for debugging.

class TestClass {};
const x = new TestClass();
const y = new TestClass();
const z = new TestClass();
queryObjects(TestClass)