JavaScript Closure, Scope

Scope

In JavaScript, objects and functions are also variables.
In JavaScript, scope is the set of variables, objects, and functions you have access to.
JavaScript has function scope: The scope changes inside functions.

Local Variables

Variables declared within a JavaScript function, become LOCAL to the function.
Local variables have local scope: They can only be accessed within the function.
Since local variables are only recognized inside their functions, variables with the same name can be used in different functions.

Local variables are created when a function starts, and deleted when the function is completed.

Global Variables

A variable declared outside a function, becomes GLOBAL.
A global variable has global scope: All scripts and functions on a web page can access it.
In Browser JS Global scope is window

Automatically Global

If you assign a value to a variable that has not been declared (var), it will automatically become a GLOBAL variable.
This code example will declare carName as a global variable, even if it is executed inside a function.

Lifetime of JavaScript Variables

The lifetime of a JavaScript variable starts when it is declared.
Local variables are deleted when the function is completed.
Global variables are deleted when you close the page.
Function arguments (parameters) work as local variables inside functions.

JavaScript Hoisting

Hoisting is JavaScript's default behavior of moving declarations to the top
In JavaScript, a variable can be declared after it has been used
In other words: a variable can be used before it has been declared
Hoisting is JavaScript's default behavior of moving all declarations to the top of the current scope (to the top of the current script or the current function).

x = 6;
x = x * 2 + 1;
var x;

var x;
x = 6;
x = x * 2 + 1;

The same

Use Strict

"use strict"; Defines that JavaScript code should be executed in "strict mode"
The purpose of "use strict" is to indicate that the code should be executed in "strict mode"
With strict mode, you can not, for example, use undeclared variables

"use strict";
x = 3.14;       // This will cause an error (x is not defined)

Closure

JavaScript variables can belong to the local or global scope
Private variables can be made possible with closures
A closure is created when an inner function is made accessible from outside of the function that created it

Nested Functions

All functions have access to the global scope.
In fact, in JavaScript, all functions have access to the scope "above" them.
JavaScript supports nested functions. Nested functions have access to the scope "above" them.
In this example, the inner function plus() has access to the counter variable in the parent function:

return function

self-invoking

CLOSURE modules

Recursion

Recursion is an important programming technique, in which a function calls itself

Validation

http://www.jslint.com/ JSLint

http://jshint.com/ JSHint

Home work

https://learn.javascript.ru/functions-closures Замыкания, область видимости

John Resig - Secrets of the JavaScript Ninja - Книга

http://gabdrahimov.ru/javascript-oglavlenie JS Учебник

http://habrahabr.ru/post/38642/ Замыкания в JavaScript

https://developer.mozilla.org/ru/docs/Web/JavaScript/Closures Замыкания

Class work

You can find in the OneDrive folder