Are trailing commas in arrays and objects part of the spec?

Question

Are trailing commas standard in JavaScript, or do most browsers like Chrome and Firefox just tolerate them?

I thought they were standard, but IE8 puked after encount

Answer 1

You can find the specification for javascript (aka ECMA Script) here. You can find the relevant definition for arrays on page 63 and as Felix noted, the object definition a couple of pages later on page 65.

While this specification says it is fine to have a trailing , I don't know if that would be true looking back a few versions. As you've noted IE8- will crap itself if you leave a trailing comma but Chrome and FF handle it fine.