Javascript RegExp for splitting text into sentences and keeping the delimiter

You need to use match not split.

Try this.

var str = "I like turtles. Do you? Awesome! hahaha. lol!!! What's going on????";
var result = str.match( /[^\.!\?]+[\.!\?]+/g );

var expect = ["I like turtles.", " Do you?", " Awesome!", " hahaha.", " lol!!!", " What's going on????"];
console.log( result.join(" ") === expect.join(" ") )
console.log( result.length === 6);

Try this instead:-

sentences = text.split(/[\\.!\?]/);

? is a special char in regular expressions so need to be escaped.

Sorry I miss read your question - if you want to keep delimiters then you need to use match not split see this question

The following is a small addition to Larry's answer which will match also paranthetical sentences:

text.match(/\(?[^\.\?\!]+[\.!\?]\)?/g);

applied on:

text = "If he's restin', I'll wake him up! (Shouts at the cage.) 
'Ello, Mister Polly Parrot! (Owner hits the cage.) There, he moved!!!"

giveth:

["If he's restin', I'll wake him up!", " (Shouts at the cage.)", 
" 'Ello, Mister Polly Parrot!", " (Owner hits the cage.)", " There, he moved!!!"]