Web Design in a Nutshell, 3rd Edition

Variables

Though not a strictly typed language, in JavaScript , you still need to declare variables before you begin using them. That said, you have a lot of flexibility in how you name and declare your variables.

Variables are declared using the reserved keyword var. Variable names can be any length and contain numbers, letters, and certain non-alphanumerics. Arithmetic operators (+, −, *, /) and quotes (' and ") need to be avoided in variable names . You also need to watch that your variable names do not conflict with JavaScript’s reserved keywords (this, for, function, etc.). A text editor with a good syntax highlighter should help you avoid those pitfalls.

Variable names can be written in numerous cases and styles. And as JavaScript is case-sensitive, each of the following would be a unique variable:

    var MYVAR; // uppercase
    var myvar; // lowercase
    var myVar; // camel case
    var MyVar; // initial caps
    var MyVaR; // mixed case

It is common practice to separate words in multiword variable (or function) names with an underscore or to write them in “camelCase”:

    var my_cat;
    var myCat;

You may consider writing all variables using one convention and all function names using the other to make it easier to distinguish them at a glance:

    var my_variable;
    function myFunction( ){ ... }

Variables can also have their values assigned when they are declared:

    var cat = 'Sabine';

or not:

    var cat;

You can also declare multiple variables (again with or without value assignment) simultaneously:

 var girl_cat ...