Window and this & scope :

• Whenever you create any JS file, then automatically attached to the window object..
• global environment context, variables and functions are present in the window object..
• window === this ---> true

Accessing the variables :

console.log(Window.variablename)

console.log(variablename)

console.log(this.variablename)

• JavaScript is a loosely typed or weakly typed language. So it means you can change the type also.

Example:

var v = 10;
console.log(v) // it will print 10
v = " shivaji";
console.log(v)    // it will print shivaji

undefined vs not defined :

Undefined:

• It is a special keyword.
• Undefined is like a special placeholder that is kept inside the variables.

Not defined:

• accessing the variable or functions without declaring...
• Not defined is a reference error.