Scope

The scope defines where variables and functions are accessible inside of your program. In JavaScript, there are two kinds of scope - global scope, and function scope. According to the official spec.

// Function scope
function iHaveScope() {
  // local function scope
  function iHaveNestedScope() {
    // nested local function scope
  }
}

Block scopes are what you get when you use if statements, for statements, and the like. You can also use them stand-alone with a simple begin-end curly braces {}, not to be confused with empty object literals.

// Block scope
var a = {} // empty object literal
{ var a } // undefined object in a block scope
if (3 == '3') {
  // block scope for the if statement
}
for (var i=0; i<10; i++) {
  // block scope for the for statement
}

Global JavaScript Variables

A variable declared outside a function becomes GLOBAL. A global variable has a global scope: All scripts and functions on a web page can access it.

var carName = "Volvo";
// code here can use carName
function myFunction() {
  // code here can also use carName
}