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JS Technical Documentation
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index.html
<!--
Hello Camper!
For now, the test suite only works in Chrome! Please read the README below in the JS Editor before beginning. Feel free to delete this message once you have read it. Good luck and Happy Coding!
- The freeCodeCamp Team
-->
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>JS Documentation</title>
<link rel="stylesheet" href="index.css" />
</head>
<body>
<!-- Site Title -->
<div class="site-grid">
<div class="title">
<h1>JavaScript Documentation</h1>
</div>
<!-- Site Sidebar -->
<div class="sidebar">
<header>Contents</header>
<a href="#1">Introduction</a>
<a href="#2">Prerequisites</a>
<a href="#3">JavaScript vs. Java</a>
<a href="#4">"Hello World"</a>
<a href="#5">Variables</a>
<a href="#6">Declaring Variables</a>
<a href="#7">Variable Scope</a>
<a href="#8">Global Variables</a>
<a href="#9">Constants</a>
<a href="#10">Data Types</a>
<a href="#11">If...else Statements</a>
<a href="#12">While Loops</a>
<a href="#13">Function Declarations</a>
<a class="last" href="#14">Reference</a>
</div>
<!-- Site Main Content -->
<main class="main" id="main-doc">
<section class="section-item" id="1">
<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>
<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>
<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.123
</li>
</ul>
</article>
</section>
<section class="section-item" id="2">
<header>Prerequisites</header>
<article>
<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>
</article>
</section>
<section class="section-item" id="3">
<header>JavaScript vs. 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 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>
</article>
</section>
<section class="section-item" id="4">
<header>"Hello World"</header>
<article>
<p>
To get started with writing JavaScript, open the Scratchpad and
write your first "Hello world" JavaScript code:
</p>
<code>function greetMe(yourName) { alert("Hello " + yourName); }
greetMe("World");
</code>
<p>
Select the code in the pad and hit Ctrl+R to watch it unfold in
your browser!
</p>
</article>
</section>
<section class="section-item" id="5">
<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 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>
</article>
</section>
<section class="section-item" id="6">
<header>Declaring Variables</header>
<article>
<p>You can declare a variable in three ways:</p>
<p>With the keyword var. For example,</p>
<code> var x = 42.</code>
<p>
This syntax can be used to declare both local and global
variables.
</p>
<p>By simply assigning it a value. For example,</p>
<code> x = 42.</code>
<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>
<code> let y = 13.</code>
<p>
This syntax can be used to declare a block scope local variable.
See Variable scope below.
</p>
</article>
</section>
<section class="section-item" id="7">
<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 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>
<code>if (true) { var x = 5; } console.log(x); // 5</code>
<p>
This behavior changes, when using the let declaration introduced
in ECMAScript 2015.
</p>
<code
>if (true) { let y = 5; } console.log(y); // ReferenceError: y is
not defined</code
>
</article>
</section>
<section class="section-item" id="8">
<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, if a variable called
phoneNumber is declared in a document, you can refer to this
variable from an iframe as parent.phoneNumber.
</p>
</article>
</section>
<section class="section-item" id="9">
<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>
<code>const PI = 3.14;</code>
<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>
<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
>
<p>
However, object attributes are not protected, so the following
statement is executed without problems.
</p>
<code
>const MY_OBJECT = {"key": "value"}; MY_OBJECT.key =
"otherValue";</code
>
</article>
</section>
<section class="section-item" id="10">
<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>
<li>
null. A special keyword denoting a null value. Because
JavaScript is case-sensitive, null is not the same as Null,
NULL, or any other variant.
</li>
<li>
undefined. A top-level property whose value is undefined.
</li>
<li>Number. 42 or 3.14159.</li>
<li>String. "Howdy"</li>
<li>
Symbol (new in ECMAScript 2015). A data type whose instances
are unique and immutable.
</li>
</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="section-item" id="11">
<header>If...else Statements</header>
<article>
<p>
Use the if statement to execute a statement if a logical condition
is true. Use the optional else clause to execute a statement if
the condition is false. An if statement looks as follows:
</p>
<code>if (condition) { statement_1; } else { statement_2; }</code>
<p>
condition can be any expression that evaluates to true or false.
See Boolean for an explanation of what evaluates to true and
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>
<code
>if (condition_1) { statement_1; } else if (condition_2) {
statement_2; } else if (condition_n) { statement_n; } else {
statement_last; }</code
>
<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, it's good practice to always use block statements,
especially when nesting if statements:
</p>
<code
>if (condition) { statement_1_runs_if_condition_is_true;
statement_2_runs_if_condition_is_true; } else {
statement_3_runs_if_condition_is_false;
statement_4_runs_if_condition_is_false; }</code
>
<p>
It is 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>
<code>if (x = y) { /* statements here */ }</code>
<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>
<code>if ((x = y)) { /* statements here */ }</code>
</article>
</section>
<section class="section-item" id="12">
<header>While Loops</header>
<article>
<p>
A while statement executes its statements as long as a specified
condition evaluates to true. A while statement looks as follows:
</p>
<code>while (condition) statement</code>
<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>
<p>Example:</p>
<p>
The following while loop iterates as long as n is less than three:
</p>
<code>var n = 0; var x = 0; while (n < 3) { n++; x += n; }</code>
<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>
<li>After the second pass: n = 2 and x = 3</li>
<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>
<section class="section-item" id="13">
<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>
<li>
A list of arguments to the function, enclosed in parentheses and
separated by commas.
</li>
<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>
<code>function square(number) { return number * number; }</code>
<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 returned by the function.
</p>
<code>return number * number;</code>
<p>
Primitive parameters (such as a number) are passed to functions by
value; the value is passed to the 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="section-item" id="14">
<header>Reference</header>
<article>
<ul>
<li>
All the documentation in this page is taken from
<a
href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide"
target="_blank"
>MDN</a
>
</li>
</ul>
</article>
</section>
</main>
<footer class="footer"></footer>
</div>
</body>
</html>
Raw
script.babel
// !! IMPORTANT README:
// You may add additional external JS and CSS as needed to complete the project, however the current external resource MUST remain in place for the tests to work. BABEL must also be left in place.
/***********
INSTRUCTIONS:
- Select the project you would
like to complete from the dropdown
menu.
- Click the "RUN TESTS" button to
run the tests against the blank
pen.
- Click the "TESTS" button to see
the individual test cases.
(should all be failing at first)
- Start coding! As you fulfill each
test case, you will see them go
from red to green.
- As you start to build out your
project, when tests are failing,
you should get helpful errors
along the way!
************/
// PLEASE NOTE: Adding global style rules using the * selector, or by adding rules to body {..} or html {..}, or to all elements within body or html, i.e. h1 {..}, has the potential to pollute the test suite's CSS. Try adding: * { color: red }, for a quick example!
// Once you have read the above messages, you can delete all comments.
Raw
style.css
* {
box-sizing: border-box;
margin: 0px;
padding: 0;
font-family: sans-serif;
}
.site-grid {
display: grid;
grid-template-columns: 15vw 85vw;
grid-template-rows: 10vh 88vh 2vh;
grid-template-areas:
"title title"
"sidebar main"
"footer footer";
}
.title {
grid-area: title;
background-color: lemonchiffon;
}
.sidebar {
grid-area: sidebar;
background-color: lemonchiffon;
}
.main {
grid-area: main;
background-color: lemonchiffon;
}
.footer {
grid-area: footer;
background-color: mediumaquamarine;
border-top: 1px solid black;
}
/* Title CSS */
div .title {
border-bottom: 1px solid black;
position: sticky;
}
h1 {
text-align: center;
margin-top: 3vh;
}
/* Sidebar CSS */
.sidebar {
display: flex;
flex-direction: column;
position: sticky;
border-right: 1px solid black;
overflow-y: auto;
min-width: fit-content;
}
.sidebar header {
font-size: 1.75rem;
flex-grow: 1.1;
padding-top: 15px;
text-align: center;
font-weight: 500;
}
.sidebar a {
border-top: 1px solid black;
flex-grow: 1;
padding-left: 15px;
padding-top: 15px;
font-size: 1.25rem;
}
.sidebar .last {
}
/* Main content CSS */
main {
overflow-y: auto;
}
section header {
font-size: 2.25rem;
margin: 1rem 1.5rem 2rem 1.5rem;
}
article {
line-height: 1.25rem;
}
article p {
margin: 1rem 3rem 0 3rem;
text-align: justify;
}
article li {
margin: 1rem 3rem 0 10rem;
}
code {
background-color: #ccc8c8;
display: block;
white-space: pre;
min-width: 60%;
width: fit-content;
line-height: 1.5rem;
min-height: 50px;
padding: 0.75rem 5rem 0.5rem 1rem;
margin-left: 5rem;
margin-top: 1rem;
border-radius: 5px;
}
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