Javascript split function not correct worked with specific regex

Well, this is ridiculous to avoid the lack of lookbehind but seems to get the correct result.

"\\,str\\,i,ing".split('').reverse().join('').split(/,(?=[^\\])/).map(function(a){
    return a.split('').reverse().join('');
}).reverse();

//=> ["\,str\,i", "ing"]

Not sure about your expected output but you are specifying string not a regex, use:

var arr = "\,str\,i,ing".split(/[^\\],/, 2);
console.log(arr);

To split using regex, wrap your regex in /..../

This is not easily possible with js, because it does not support lookbehind. Even if you'd use a real regex, it would eat the last character:

> "xyz\\,xyz,xyz".split(/[^\\],/, 2)
["xyz\\,xy", "xyz"]

If you don't want the z to be eaten, I'd suggest:

var str = "....";
return str.split(",").reduce(function(res, part) {
    var l = res.length;
    if (l && res[l-1].substr(-1) == "\\" || l<2)
//      ^                        ^^          ^
//  not the first         was escaped      limit
        res[l-1] += ","+part;
    else
        res.push(part);
    return;
}, []);

Reading between the lines, it looks like you want to split a string by , characters that are not preceded by \ characters.

It would be really great if JavaScript had a regular expression lookbehind (and negative lookbehind) pattern, but unfortunately it does not. What it does have is a lookahead ((?=) )and negative lookahead ((?!)) pattern. Make sure to review the documentation.

You can use these as a lookbehind if you reverse the string:

var str,
    reverseStr,
    arr,
    reverseArr;
//don't forget to escape your backslashes
str = '\\,str\\,i,ing';

//reverse your string
reverseStr = str.split('').reverse().join('');

//split the array on `,`s that aren't followed by `\`
reverseArr = reverseStr.split(/,(?!\\)/);

//reverse the reversed array, and reverse each string in the array
arr = reverseArr.reverse().map(function (val) {
    return val.split('').reverse().join('');
});

You picked a tough character to match- a forward slash preceding a comma is apt to disappear while you pass it around in a string, since '\,'==','...

var s= 'My dog, the one with two \\, blue \\,eyes, is asleep.';
var a= [], M, rx=/(\\?),/g;
while((M= rx.exec(s))!= null){
    if(M[1]) continue;
    a.push(s.substring(0, rx.lastIndex-1));
    s= s.substring(rx.lastIndex);
    rx.lastIndex= 0;
};
a.push(s);


/*  returned value: (Array)
My dog 
the one with two \, blue \,eyes 
is asleep.
*/

Find something which will not be present in your original string, say "@@@". Replace "\\," with it. Split the resulting string by ",". Replace "@@@" back with "\\,".

Something like this:

<script type="text/javascript">
   var s1 = "\\,str\\,i,ing";
   var s2 = s1.replace(/\\,/g,"@@@");
   console.log(s2);
   var s3 = s2.split(",");
   for (var i=0;i<s3.length;i++)
   {
       s3[i] = s3[i].replace(/@@@/g,"\\,");
   }
   console.log(s3);
 </script>

See JSFiddle