var usage Javascript

var testFn = function(){
    var arr = [];
    this.addToArray = function(obj){
        arr.push(obj);
    };
    this.triggerArray = function(){
        for(i = 0; i < arr.length; i++){
            arr[i].apply();
        }
    }
}

var instance1 = new testFn();
var instance2 = new testFn();
instance1.addToArray(function(){console.log("Instance 1 - First Function")});
instance2.addToArray(function(){console.log("Instance 2 - First Function")});
instance2.addToArray(function(){console.log("Instance 2 - Second Function")});
instance2.addToArray(instance1.addToArray.bind(instance1));

//---------------Test-------------//
instance2.triggerArray();
// gets into for loop,
// instance2.arr has three function objects
// at i = 0 , executes - Instance 2 - First Function
// at i = 1 , executes - Instance 2 - Second Function
// at i = 2 , calls Instance 1 triggerArray()
    // gets into for loop
    // instance1.arr has one function object
    // at i = 0 , executes - Instance 1 - First Function
    // comes out of loop when i = 1 not less then arr.length
// whats the i value now at instance 2
// it checks in local scope, closure scope, didn't find it , so checks in global scope
// at global scope i value will be 1 a
// at i = 1 , executes - Instance 2 - Second Function
// at i = 2 , calls Instance 1 triggerArray()
    // goes into infinite loop

// Thus its important to declare i as var i in for-loop
// in javascript if var is not declared , it puts in global scope