Support for ES2018 Regular Expressions

I’m getting a Warning for a Regular Expression but it actually works.

Javascript code:

function getIframesSources(html) {
	return html.match(/(?<=<iframe.* src\s*=\s*").*?(?=")/gmi);
}

Warning thrown by Closure Compiler v20180716: WARNING - Malformed Regular Expression: Malformed parenthetical: (?<=<iframe.* src\s*=\s*").*?(?=")

Working RegEx test: https://regex101.com/r/4YyzKP/1

[brad4d]

We’ve done all we plan to do for supporting the RegExp features added in ES_2018. closure-compiler will recognize them and not choke on them. However, if your output language is earlier than ES_2018, then the compiler will issue a suppressible error to tell you that it cannot transpile the new RegExp features to make them work where they are not natively supported.

[brad4d]

@MatthewMerrill will be working on this in the next few weeks.