This document discusses variables in JavaScript. It defines variables as places to store values that can later be used, analogous to boxes that can dynamically resize to hold different data types. It outlines rules for naming variables, including that names must start with a letter, underscore, or dollar sign, and cannot be reserved words. The document also notes that JavaScript is a weakly typed language, meaning variables do not require explicit data type declaration.

1. JavaScript
Variables
Charles Russell
Bennu Bird Media

2. Statement and
Expressions
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A Statement requests an action.
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An Expression sets a value.
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Variables are used in both
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They are passed into functions and used to control
branching and iteration
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They can be the target of the expression or the value
of the expression
– In computer books you may see L value and R Value when
referring to expressions

3. So What are they
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A variable a just a place to put things you want to
use later. A good anology would be a box
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In JavaScript anything can go into a box
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In this language the boxes are a little magical
– Boxes can resize themselves to hold anything you put in
them.
– Dumping from one box into another makes what was
already the box you are dumping into vanish

4. Labeling the Boxes
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To name a variable just type a name and set a
value. You will not only named it you have
created and sized it.
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var myVariable=“Some really cool stuff“;
– Note the var while not required leaving it off has some
implications that we will get into later
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Another word for name is identifier and in computer
books it is more common to use identifier.
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In general you can use any name you want, but
there are a few rules

5. Whats in a name
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In Javascript a name must begin with a letter _ or
$
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Names beginning with _ are generally used by
the system
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Names beginning with $ are commonly used by
libraries
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After the first character you can use as many
letters and numbers $ and _ as you want after
that
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Name are case sensitive Name and name are not

6. Forbiden Names
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Use of these words as names will cause an error
abstract debugger final instanceof protected throws
boolean default finally int public transient
break delete float interface return true
byte do for let short try
case double function long static typeof
catch else goto native super var
char enum if new switch void
class export implements null synchronized volatile
const extends import package this while
continue false in private throw with

7. Names with Baggage
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Some names are used by Javascript
implementations and while legal should be
avoided. A partial list is below for more go to
http://www.javascripter.net/faq/reserved.htm
alert clearInterval decodeURIComponent
all clearTimeout defaultStatus
anchor clientInformation document
anchors close element
area closed elements
Array confirm embed
assign constructor embeds
blur crypto encodeURI
button Date encodeURIComponent
checkbox decodeURI escape

8. Weak Typing
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JavaScript is a weakly typed language
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This does not mean that it is type unaware
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This means that you do not have to declare the
type of the variable

9. Summary
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Variables are used in statements and expressions
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The are just a way to store things for later use
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There are rules to names
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You cant use reserved words as names
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Some legal names are not a good Idea
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Java Script is a weekly typed language

10. Next Datatypes