Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition

Variables

No particular character identifies a variable in JavaScript, the way the dollar sign ($) does in PHP. Instead, variables use the following naming rules:

• A variable may include only the letters a-z, A-Z, 0-9, the $ symbol, and the underscore (_).

• No other characters, such as spaces or punctuation, are allowed in a variable name.

• The first character of a variable name can be only a-z, A-Z, $, or _ (no numbers).

• Names are case-sensitive. Count, count, and COUNT are all different variables.

• There is no set limit on variable name lengths.

And yes, you’re right, that is the $ there in that list. It is allowed by JavaScript and may be the first character of a variable or function name. Although I don’t recommend keeping the $s, this does mean that you can port a lot of PHP code to JavaScript quickly.

String Variables

JavaScript string variables should be enclosed in either single or double quotation marks, like this:

greeting = "Hello there"
warning  = 'Be careful'

You may include a single quote within a double-quoted string or a double quote within a single-quoted string, but a quote of the same type must be escaped using the backslash character, like this:

greeting = "\"Hello there\" is a greeting"
warning  = '\'Be careful\' is a warning'

To read from a string variable, you can assign it to another one, like this:

newstring = oldstring

or you can use it in a function, like this:

status = "All systems are working"
document.write(status)

Numeric Variables

Creating a numeric variable is as simple ...