New in JavaScript 1.5

From MDC

JavaScript version 1.5 provided the following new features and enhancements:

Runtime errors
Runtime errors are now reported as exceptions.

Number formatting enhancements
Number formatting has been enhanced to include Number.prototype.toExponential, Number.prototype.toFixed and Number.prototype.toPrecision methods. See the Number Object page.

Regular expression enhancements
The following regular expression enhancements have been added:

• Quantifiers — +, *, ? and {} — can now be followed by a ? to force them to be non-greedy. See the entry for ? on the Writing a Regular Expression Pattern page.
• Non-capturing parentheses, (?:x) can be used instead of capturing parentheses, (x). When non-capturing parentheses are used, matched subexpressions are not available as back-references. See the entry for (?:x) on the Writing a Regular Expression Pattern page.
• Positive and negative lookahead assertions are supported. Both assert a match depending on what follows the string being matched. See the entries for x(?=y) and x(?!y) on the Writing a Regular Expression Pattern page.
• The m flag has been added to specify that the regular expression should match over multiple lines. See the Executing a Global Search, Ignoring Case, and Considering Multiline Input page.

Conditional function declarations
Functions can now be declared inside an if clause. See the Defining Functions page.

Function expressions
Functions can now be declared inside an expression. See the Defining Functions page.

Multiple catch clauses
Multiple catch clauses in a try...catch statement are supported. See The catch Block page.

Getters and Setters
JavaScript writers can now add getters and setters to their objects. This feature is available only in the C implementation of JavaScript. See the Defining Getters and Setters page.

Constants
Read only named constants are supported. This feature is available only in the C implementation of JavaScript. See the Constants page.