Pass in a string to validate if it would work in ECMA-262, aka JavaScript.
The information for what is valid and what isn't comes from http://www.regular-expressions.info/javascript.html.
Pass in either a string or a Regexp:
require 'ecma-re-validator'
re = "[Ss]mith\\\\b"
EcmaReValidator.valid?(re) # true
re = /(?<=a)b/
EcmaReValidator.valid?(re) # false--lookbehinds don't exist in JS