JavaScript
Variables
In all programs
and all programming languages we have to keep track of many pieces of data. So we create variables to store data
inside them.
The variable
is a container, its grabbing a little piece of data (information) and giving it
a name so we can use it. Creating variables is very easy. Just type var variablename;
EXAMPLE:
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div
id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var bar;
</script>
</body>
</html>
The name for
your variable must be written as one word, no spaces are allowed. It can starts
with word, letter, underscore, dollar sign, but you cannot start with number.
The above
value hasn’t value, so this variable is undefined.
Now we have
to define our variable, to set value.
Example:
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var bar;
bar = 20;
console.log(bar);
</script>
</body>
</html>
The equal
sign setting variable bar to 300.
You can also
combine them into one statement:
Example:
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div
id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var bar = 20;
console.log(bar);
</script>
</body>
</html>
The word var
is not required in JavaScript. But leaving var may lead to unexpended behavior.
Variable name
are case-sensitive. So var x; and var X; will be different variables.
You can also
create multiple variables nested in one line:
Example:
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div
id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var bar,
head, x, y, foo;
</script>
</body>
</html>
You can
assign values to them:
Example:
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div
id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var bar = 40,
head = "Hello", x = "This is x variable", y = true;
</script>
</body>
</html>
But better
practice is to add one variable to one line because it will be hard to read.
Variables can
store numbers, Boolean values (true or false, always in lowercase) – you don’t
need quotes around them, you can also add piece of text (string) – you can use
either double quotes or you can use single quotes, no matter which you use, but
don’t mix them. The most common practice is to you double quotes but that’s
your own choice.
Example:
<html>
<head>
<title>Untitled
Document</title>
</head>
<body>
<div
id="demo">
<h1>This
is a heading.</h1>
<p>This
is a paragraph.</p>
</div>
<script>
var bar=
500; // number in
variable
var x =
"Hello World"; //
Piece if text(String)
var y =
true; // Boolean value
true
var demo =
false; // Boolean value
false
</script>
</body>
</html>
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