JavaScript: The Definitive Guide, 6th Edition

JavaScript Subsets

Most language subsets are defined to allow the secure execution of untrusted code. There is one interesting subset defined for different reasons. We’ll cover that one first, and then cover secure language subsets.

The Good Parts

Douglas Crockford’s short book JavaScript: The Good Parts (O’Reilly) describes a JavaScript subset that consists of the parts of the language that he thinks are worth using. The goal of this subset is to simplify the language, hide quirks and imperfections, and ultimately, make programming easier and programs better. Crockford explains his motivation:

Most programming languages contain good parts and bad parts. I discovered that I could be a better programmer by using only the good parts and avoiding the bad parts.

Crockford’s subset does not include the with and continue statements or the eval() function. It defines functions using function definition expressions only and does not include the function declaration statement. The subset requires the bodies of loops and conditionals to be enclosed in curly braces: it does not allow the braces to be omitted if the body consists of a single statement. It requires any statement that does not end with a curly brace to be terminated with a semicolon.

The subset does not include the comma operator, the bitwise operators, or the ++ and -- operators. It also disallows == and != because of the type conversion they perform, requiring use of === and !== instead.

Since JavaScript does not have block scope, ...