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<nav id="navbar" class="navbar">
<header class="navbar-header">JS Documentation</header>
<a href="#introduction" class="nav-link">Introduction</a> <br />
<a href="#what_you_should_already_know" class="nav-link"
>What You Should Already Know</a
><br />
<a href="#JavaScript_&_Java" class="nav-link">JavaScript & Java</a><br />
<a href="#Hello_world" class="nav-link">Hello World</a><br />
<a href="#Variables" class="nav-link">Variables</a><br />
<a href="#Declaring_variables" class="nav-link">Declaring Variables</a
><br />
<a href="#Variable_scope" class="nav-link">Variable Scope</a><br />
<a href="#global_variables" class="nav-link">Global_variables</a><br />
<a href="#constants" class="nav-link">Constants</a><br />
</nav>
<main id="main-doc">
<section class="main-section" id="introduction">
<header>Introduction</header>
<p>
JavaScript is a cross-platform, object-oriented scripting language. It
is a small and lightweight language. Inside a host environment (for
example, a web browser), JavaScript can be connected to the objects of
its environment to provide programmatic control over them.
</p>
<p>
JavaScript contains a standard library of objects, such as Array,
Date, and Math, and a core set of language elements such as operators,
control structures, and statements. Core JavaScript can be extended
for a variety of purposes by supplementing it with additional objects;
for example:
</p>
<ul>
<li>
Client-side JavaScript extends the core language by supplying
objects to control a browser and its Document Object Model (DOM).
For example, client-side extensions allow an application to place
elements on an HTML form and respond to user events such as mouse
clicks, form input, and page navigation.
</li>
<br />
<br />
<li>
Server-side JavaScript extends the core language by supplying
objects relevant to running JavaScript on a server. For example,
server-side extensions allow an application to communicate with a
database, provide continuity of information from one invocation to
another of the application, or perform file manipulations on a
server.
</li>
</ul>
<br />
<br />
</section>
<section class="main-section" id="what_you_should_already_know">
<header>What you should already know</header>
<p>This guide assumes you have the following basic background</p>
<ul>
<li>
A general understanding of the Internet and the World Wide Web
(WWW).
</li>
<li>Good working knowledge of HyperText Markup Language (HTML).</li>
<li>
Some programming experience. If you are new to programming, try one
of the tutorials linked on the main page about JavaScript.
</li>
</ul>
</section>
<br />
<br />
<section class="main-section" id="JavaScript_&_Java">
<header>JavaScript & Java</header>
<p>
JavaScript and Java are similar in some ways but fundamentally
different in some others. The JavaScript language resembles Java but
does not have Java's static typing and strong type checking.
JavaScript follows most Java expression syntax, naming conventions and
basic control-flow constructs which was the reason why it was renamed
from LiveScript to JavaScript.
</p>
<p>
In contrast to Java's compile-time system of classes built by
declarations, JavaScript supports a runtime system based on a small
number of data types representing numeric, Boolean, and string values.
JavaScript has a prototype-based object model instead of the more
common class-based object model. The prototype-based model provides
dynamic inheritance; that is, what is inherited can vary for
individual objects. JavaScript also supports functions without any
special declarative requirements. Functions can be properties of
objects, executing as loosely typed methods.
</p>
<p>
JavaScript is a very free-form language compared to Java. You do not
have to declare all variables, classes, and methods. You do not have
to be concerned with whether methods are public, private, or
protected, and you do not have to implement interfaces. Variables,
parameters, and function return types are not explicitly typed.
</p>
</section>
<br />
<br />
<section class="main-section" id="Hello_world">
<header>Hello world</header>
<p>
To get started with writing JavaScript, open the Scratchpad and write
your first "Hello world" JavaScript code:
</p>
<pre>
<code>
function greetMe(yourName) { alert("Hello " + yourName); }
greetMe("World");
</code>
</pre>
<p>
Select the code in the pad and hit Ctrl+R to watch it unfold in your
browser!
</p>
</section>
<br />
<br />
<section class="main-section" id="Variables">
<header>Variables</header>
<p>
You use variables as symbolic names for values in your application.
The names of variables, called identifiers, conform to certain rules.
</p>
<p>
A JavaScript identifier must start with a letter, underscore (_), or
dollar sign ($); subsequent characters can also be digits (0-9).
Because JavaScript is case sensitive, letters include the characters
"A" through "Z" (uppercase) and the characters "a" through "z"
(lowercase).
</p>
<p>
You can use ISO 8859-1 or Unicode letters such as å and ü in
identifiers. You can also use the Unicode escape sequences as
characters in identifiers. Some examples of legal names are
Number_hits, temp99, and _name.
</p>
</section>
<br />
<br />
<section class="main-section" id="Declaring_variables">
<header>Declaring variables</header>
<p>You can declare a variable in three ways:</p>
<p>With the keyword var. For example,</p>
<pre>
<code> var x = 42. </code>
</pre>
<p>
This syntax can be used to declare both local and global variables.
</p>
<p>By simply assigning it a value. For example</p>
<pre>
<code> x = 42. </code>
</pre>
<p>
This always declares a global variable. It generates a strict
JavaScript warning. You shouldn't use this variant.
</p>
<p>With the keyword let. For example,</p>
<pre>
<code> let y = 13. </code>
</pre>
<p>
This syntax can be used to declare a block scope local variable. See
Variable scope below.
</p>
</section>
<br />
<br />
<section class="main-selection" id="Variable_scope">
<header>Variable scope</header>
<p>
When you declare a variable outside of any function, it is called a
global variable, because it is available to any other code in the
current document. When you declare a variable within a function, it is
called a local variable, because it is available only within that
function.
</p>
<p>
JavaScript before ECMAScript 2015 does not have block statement scope;
rather, a variable declared within a block is local to the function
(or global scope) that the block resides within. For example the
following code will log 5, because the scope of x is the function (or
global context) within which x is declared, not the block, which in
this case is an if statement
</p>
<pre>
<code> if (true) { var x = 5; } console.log(x); // 5 </code>
</pre>
<p>
This behavior changes, when using the let declaration introduced in
ECMAScript 2015.
</p>
<pre>
<code>
if (true) { let y = 5; } console.log(y); // ReferenceError: y is not
defined
</code>
</pre>
</section>
<br />
<br />
<section class="main-selection" id="global_variables">
<header>Global variables</header>
<p>
Global variables are in fact properties of the global object. In web
pages the global object is window, so you can set and access global
variables using the window.variable syntax
</p>
<p>
Consequently, you can access global variables declared in one window
or frame from another window or frame by specifying the window or
frame name. For example, if a variable called phoneNumber is declared
in a document, you can refer to this variable from an iframe as
parent.phoneNumber.
</p>
</section>
<br />
<br />
<section class="main-selection" id="constants">
<header>Constants</header>
<p>
You can create a read-only, named constant with the const keyword. The
syntax of a constant identifier is the same as for a variable
identifier: it must start with a letter, underscore or dollar sign and
can contain alphabetic, numeric, or underscore characters.
</p>
<pre>
<code>const PI = 3.14; </code>
</pre>
<p>
A constant cannot change value through assignment or be re-declared
while the script is running. It has to be initialized to a value.
</p>
<p>
The scope rules for constants are the same as those for let block
scope variables. If the const keyword is omitted, the identifier is
assumed to represent a variable.
</p>
<p>
You cannot declare a constant with the same name as a function or
variable in the same scope. For example:
</p>
<pre>
<code> // THIS WILL CAUSE AN ERROR function f() {}; const f = 5; // THIS
WILL CAUSE AN ERROR ALSO function f() { const g = 5; var g;
//statements } </code>
</pre>
<p>
However, object attributes are not protected, so the following
statement is executed without problems.
</p>
<pre>
<code> const MY_OBJECT = {"key": "value"}; MY_OBJECT.key =
"otherValue";
</code>
</pre>
</section>
</main>