Chapter 3

Language Basics


  • Reviewing syntax
  • Working with data types
  • Working with flow-control statements
  • Understanding functions

At the core of any language is a description of how it should work at the most basic level. This description typically defines syntax, operators, data types, and built-in functionality upon which complex solutions can be built. As previously mentioned, ECMA-262 defines all of this information for JavaScript in the form of a pseudolanguage called ECMAScript.

ECMAScript as defined in ECMA-262, third edition, is the most-implemented version among web browsers. The fifth edition is the next to be implemented in browsers, though, as of the end of 2011, no browser has fully implemented it. For this reason the following information is based primarily on ECMAScript as defined in the third edition with changes in the fifth edition called out.


ECMAScript’s syntax borrows heavily from C and other C-like languages such as Java and Perl. Developers familiar with such languages should have an easy time picking up the somewhat looser syntax of ECMAScript.


The first concept to understand is that everything is case-sensitive; variables, function names, and operators are all case-sensitive, meaning that a variable named test is different from a variable named Test. Similarly, typeof can’t be the name of a function, because it’s a keyword (described in the next section); however, typeOf is a perfectly valid function name. ...

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