What is the different between a parameter and a local variable?

Question

Apologies for what must seem like a very stupid question.

I\'m currently working through codecadamy, and this is throwing me off:

 var greet         


        

Answer 1

Technically, there is no real difference.

Without giving you the huge background here, you have to understand that in the underlaying implementation, a special object (not a javascript object, on C/C++ level) is formed which is called Activation Object (ES3) or Lexical Environment Record (ES5).

However, this hash / object structure is used to store

• variables declared by var
• formal parameters
• function declarations

As you can see, both var variables and parameters are stored in this structure.

This construct is most likely used to have somewhat default values for not passed in arguments. In a real world example, this would probably look more like

var greeting = function( name ) {
    name = name || 'default';

    console.log( name );
};

greeting('john');  // 'john'
greeting();        // 'default'