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Intro to Regular Expressions

Regular-Expressions.info's JavaScript Guide

MSDN's Intro to Regular Expressions

Useful Validation Regexes

A natural number (positive integer): /^\d+$/

An integer: /^-?\d+$/

A float: /^-?(\d+\.?\d*|\d*\.\d+)$/

It's worth noting that these are only sanity checks and don't guarantee the base or value of the actual number (e.g. 000000.10000 would pass the float check).