Where "this" gets weird in JS

thisHell.js

function test() {
  this.arr = [1,2,4];
  this.message = "I am here";
  this.fun = function() {
  	this.arr.forEach(function(item) {
    	console.log(this.message); // will print undefined 3 times since this refers to the global object
    });
  }
}

var t = new test();
t.fun();

// In the above code, "this" WILL NOT refer to the test object but instead the global object

//to get around this, you can use a variable to store "this" when it does refer to test

// Since "this" still refers to the object, it will also get updated when using the substitute variable.

function test2() {
  var self = this;
  self.arr = [1,2,4];
  self.message = "I am here";
	self.fun = function() {
  	this.arr.forEach(function(item) {
    	console.log(self.message); // prints "I am Here" 3 times
    });
  }
}


var t2 = new test2();
t2.fun();