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javascriptregexnegative-lookbehind

Javascipt regex to get string between two characters except escaped without lookbehind

I am looking for a specific javascript regex without the new lookahead/lookbehind features of Javascript 2018 that allows me to select text between two asterisk signs but ignores escaped characters.

In the following example only the text "test" and the included escaped characters are supposed to be selected according the rules above: \*jdjdjdfdf*test*dfsdf\*adfasdasdasd*test**test\**sd* (Selected: "test", "test", "test\*")

During my research I found this solution Regex, everything between two characters except escaped characters /(?<!\\)(%.*?(?<!\\)%)/ but it uses negative lookbehinds which is supported in javascript 2018 but I need to support IE11 as well, so this solution doesn't work for me.

Then i found another approach which is almost getting there for me here: Javascript: negative lookbehind equivalent?. I altered the answer of Kamil Szot to fit my needs: ((?!([\\])).|^)(\*.*?((?!([\\])).|^)\*) Unfortuantely it doesn't work when two asterisks ** are in a row.

I have already invested a lot of hours and can't seem to get it right, any help is appreciated!

An example with what i have so far is here: https://www.regexpal.com/?fam=117350

I need to use the regexp in a string.replace call (str.replace(regexp|substr, newSubStr|function); so that I can wrap the found strings with a span element of a specific class.

Solution

  • You can use this regular expression:

    (?:\\.|[^*])*\*((?:\\.|[^*])*)\*

    Your code should then only take the (only) capture group of each match.

    Like this:

    var str = "\\*jdjdjdfdf*test*dfsdf\\*adfasdasdasd*test**test\\**sd*";
var regex = /(?:\\.|[^*])*\*((?:\\.|[^*])*)\*/g

var match;
while (match = regex.exec(str)) {
    console.log(match[1]);
}

    If you need to replace the matches, for instance to wrap the matches in a span tag while also dropping the asterisks, then use two capture groups:

    var str = "\\*jdjdjdfdf*test*dfsdf\\*adfasdasdasd*test**test\\**sd*";
var regex = /((?:\\.|[^*])*)\*((?:\\.|[^*])*)\*/g

var result = str.replace(regex, "$1<span>$2</span>");
console.log(result);

    One thing to be careful with: when you use string literals in JavaScript tests, escape the backslash (with another backslash). If you don't do that, the string actually will not have a backslash! To really get the backslash in the in-memory string, you need to escape the backslash.