Global and Local and Private Functions (Javascript)

Question

I am currently reading a book on Javascript by Pragmatic, and I\'m confused about one thing. They have a section on how to make variables global, local, or private.

Answer 1

In the context of the browser, the var keyword scopes the variable to that of the current function.

var a = 10;

var b = function(a) {
   console.log(a);  # 15
}

b(15);
console.log(a);  # 10

If you do not include the var keyword, it is assigned the scope of window and is considered global. Unless you have a very good reason to exclude it, always include the var keyword.

A variable is considered private if it only exists inside a function scope. This commonly takes the form of an anonymous function. This is not actually a private variable in the common sense of the term, it is simply a local variable.

(function() {
  var x = 10;
})();

console.log(x); #undefined