JavaScript Syntax Rules

JavaScript is a simple language, but you do need to be careful to use its syntax—the rules that define how you use the language—correctly. The rest of this book covers many aspects of JavaScript syntax, but there are a few basic rules you should understand to avoid errors.

Case Sensitivity

Almost everything in JavaScript is case sensitive, which means you cannot use lowercase and capital letters interchangeably. Here are a few general rules:

• JavaScript keywords, such as for and if, are always lowercase.

• Built-in objects, such as Math and Date, are capitalized.

• DOM object names are usually lowercase, but their methods are often a combination of capitals and lowercase. Usually capitals are used for all but the first word, as in toLowerCase and getElementById.