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<header id="JS-Documentation">
<h1>JS Documentation</h1>
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<ul>
<li><a href="#introduction" class="nav-link">Introduction</a><br /></li>
<li><a href="#what_you_should_already_know" class="nav-link">What you should already know</a><br /></li>
<li><a href="#javascript_and_java" class="nav-link">JavaScript and Java</a><br /></li>
<li><a href="#hello_world" class="nav-link">Hello world</a><br /></li>
<li><a href="#variables" class="nav-link">Variables</a><br /></li>
<li><a href="#declaring_variables" class="nav-link">Declaring variables</a><br /></li>
<li><a href="#variable_scope" class="nav-link">Variable scope</a><br /></li>
<li><a href="#global_variables" class="nav-link">Global variables</a><br /></li>
<li><a href="#constants" class="nav-link">Constants</a><br /></li>
<li><a href="#data_types" class="nav-link">Data types</a><br /></li>
<li><a href="#if...else_statements" class="nav-link">if...else statement</a><br /></li>
<li><a href="#while_statement" class="nav-link">while statement</a><br /></li>
<li><a href="#function_declarations" class="nav-link">Function declarations</a><br /></li>
<li><a href="#reference" class="nav-link">Reference</a><br /></li>
</ul>
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<main id="main-doc">
<section class="main-section" id= "introduction">
<header>Introduction</header>
<article>
<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><br>
<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>
<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>
</article>
</section>
<section class="main-section" id="what_you_should_already_know">
<header>What you should already know</header>
<article>
<span>This guide assumes you have the following basic background:</span>
<ul>
<li>A general understanding of the Internet and the World WIde Web (WWW).</li><br>
<li>Good working knowledge of HyperText Markup Language (HTML).</li><br>
<li>Some programming experience. If you are new to programming, try one of the tutorials
linked on the main page about JavaScript.</li>
</ul>
</article>
</section><!--
JavaScript and Java
--><section class="main-section" id="javascript_and_java">
<header>JavaScript and Java</header>
<article>
<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 expressions 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 explicit
typed.
</p>
</article>
</section>
<section class="main-section" id="hello_world">
<header>Hello world</header>
<article>
<p>To get started with writing Javascript, open the Scratchpad and write your first "Hello world" JavaScript code:</p>
<pre>
<code>function greetMe(your name) { alert("Hello " + yourName); }</code>
<code>greetMe("World");</code>
</pre>
<p>Select the code in the pad and hit Ctrl+R to watch it unfold in your browser!</p>
</article>
</section><!--
Variables
--><section class="main-section" id="variables">
<header>Variables</header>
<article>
<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 á and ű 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>
</article>
</section>
<section class="main-section" id="declaring_variables">
<header>Declaring variables</header>
<article>
<p>
<span>You can declare a variable in three ways:</span><br>
<span>With the keyword var. For example, </span>
</p>
<pre>
<code>var x = 42.</code>
</pre>
<p>
<span>This syntax can be used to declare both local and global variables.</span><br>
<span>By simply assigning it a value. For example,</span>
</p>
<pre>
<code>x = 42.</code>
</pre>
<p>
<span>This always declares a global variable. It generates a strict JavaScript warning.
You shouldn't use this variant.</span><br>
<span>With the keyword let. For example,</span>
</p>
<pre>
<code>let y = 13.</code>
</pre>
<span>This syntax can be used to declare a block scope local variable. See Variable below.</span>
</article>
</section>
<section class="main-section" id="variable_scope">
<header>Variable scope</header>
<article>
<p>When you declare a variable outside of any function, it is called a global variable,
because it is available to ny codre in the current document.
When you declare a vatiabler 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) { xar x = 5} console.log(x); // 5</code>
</pre>
<span>This behavior changes when the let declaration introduced in ECMAScript 2015.
</span>
<pre>
<code>if (true) { let y = 5} console.log(y); // 5 ReferenceError: y is
not defined</code>
</pre>
</article>
</section>
<section class="main-section" id="global_variables">
<header>Global variables</header>
<article>
<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, is a variable called phoneNumber is declared in a document,
you can refer to this variable from an inframe as parent phoneNumber.
</p>
</article>
</section><!--
Constants
--><section class="main-section" id="constants">
<header>Constants</header>
<article>
<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 redeclared 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 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 </code><br>
<code>CAUSE AN ERROR ALSO function () { const g = 5; var g; // statements}</code>
</pre>
<p>However, object attributes are not protected, so the following is executed without problems.</p>
<pre>
<code>constant MY_OBJECT = ("key": "value"); MY_OBJECT.key = "otherValue";</code><br>
</pre>
</article>
</section><!--
Data Types
--><section class="main-section" id="data_types">
<header>Data types</header>
<article>
<p>The latest ECMAScript standard defines seven data types:</p>
<ul>
<li>Six data types that are primitives:
<ul>
<li>Boolean. true and false </li><br>
<li>null. A special keyword denoting a null value. Because JavaScript is case-sensitive, null is not
same as Null, NULL, or any other variant.</li><br>
<li>undefined. A top-level property whose value is undefined.</li><br>
<li>Number. 42 or 3.14159</li><br>
<li>String. "Howdy"</li><br>
<li>Symbol (new in ECMAScript 2015). A data type whose instances are unique and immutable.</li><br>
</ul>
</li>
<li>and Object</li>
</ul>
<p>Although these data types are a relatively small amount, they enable you to perform useful functions with your
applications. Objects and functions are the other fundamental elements in the language. You can think of objects as
named containers for values, and functions as procedures that your application can perform.
</p>
</article>
</section>
<section class="main-section" id="if...else_statement">
<header>if...else statement</header>
<article>
<p>Use the if statement to execute a statement if a logical condition is true. Use the optional else to
execute a statement if the condition is false. An if statement looks as follows:
</p>
<pre>
<code>if (condition) { statement_1; } else { statement_2; }</code><br>
</pre>
<p>condition can be any expression that evaluates to true or false. See Boolean for an explanation of what
evaluates to true anad false. If condition evaluates to true, statement_1 is executed; otherwise, statement_2
is executed. statement_1 and statement_2 can be any statement, including further nested if statements.
</p>
<p>You may also compound the statements using else if to have multiple conditions tested in sequence, as follows:</p>
<pre>
<code>if (condition_1) { statement_1; } else if (condition_2) {statement_2;}</code><br>
<code>else if (condition_n) { statement_n; } else { statement_last; }</code>
</pre>
<p>In the case of multiple conditions only the first logical condition which evaluates to true will be executed.
To execute multiple statements, group them within a block statement ({...}). In general, its good practice to
always use block statements, especially when nesting if statements:
</p>
<pre>
<code>if (condition) { statement_1_runs_if_condition_is_true;</code><br>
<code>statement_2_runs_if_condition_is_true; } else {</code><br>
<code>statement_3_runs_if_condition_is_false;</code>
<code>statement_4_runs_if_condition_is_false; }</code>
</pre>
<p>Is it advisable to not use simple assignments in a conditional expression, because the assignment can be confused
with equality when glancing over the code. For example, do not use the following code:
</p>
<pre>
<code>if (x = y) { /* statements here */ }</code><br>
</pre>
<p>If you need to use an assignment in a conditional expression, a common practice is to put additional parentheses
around the assignment. For example:
</p>
<pre>
<code>if ((x = y)) { /* statements here */ }</code><br>
</pre>
</article>
</section>
<section class="main-section" id="while_statement">
<header>while statement</header>
<article>
<p>A while executed its statements as long as a specified condition evaluates to true. A while statement
looks as follows:</p>
<pre>
<code>while (condition) statement</code><br>
</pre>
<p>If the condition becomes false, statement within the loop stops executing and control passes to the
statement following the loop.</p>
<p>The condition test occurs before statement in the loop is executed. If the condition returns true, statement is
executed and the condition is tested again. If the condition returns false, execution stops and control is passed
to the statement following while.</p>
<p>To execute multiple statements, use a block statement ({...}) to group those statements.</p>
<span>Example:</span>
<p>The following while loop iterates as long as n is less than three:</p>
<pre>
<code>var n = 0; var x = 0; while n < 3 { n++; x += n; }</code>
</pre>
<p>With each iteration, the loop increments n and adds that value to x. Therefore, x and n take on the following values: </p>
<ul>
<li>After the first pass: n = 1 and x = 1</li><br>
<li>After the second pass: n = 2 and x = 3</li><br>
<li>After the third pass: n = 3 and x = 6</li>
</ul>
<p>After completing the third pass, the condition n < 3 is no longer true, so the loop terminates></p>
</article>
</section><!--
Function Declarations
--><section class="main-section" id="function_declarations">
<header>Function declarations</header>
<article>
<p>A function definition (also called a function declaration, or function statement) consists of the function keyword, followed by: </p>
<ul>
<li>The name of the function</li><br>
<li>A list arguments to the function, enclosed in parentheses and separated by commas.</li><br>
<li>The JavaScript statements that define the function, enclosed in curly brackets, {}.</li>
</ul>
<p>For example, the following code defines a simple function named square:</p>
<pre>
<code>function square(number) { return number * number; }</code>
</pre>
<p>The function square takes one argument, called number. The function consists of one statement that says to return
the argument of the function (that is, number) multiplied by itself. The return statement specifies the value by
the function.
</p>
<pre>
<code>return number * number;</code>
</pre>
<p>Primitive parameter (such as a number) are passed to function, but if the function changes the value of the
parameter, this change is not reflected globally or in the calling function.
</p>
</article>
</section>
<section class="main-section" id="reference">
<header>Reference</header>
<ul><li>All the documentation in this page is taken from <a class="reference-mdn">MDN</a></li><br></ul>
</section>
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