Javascript And Regex: Split String And Keep The Separator

July 30, 2023 Post a Comment

I have a string: var string = 'aaaaaa† bbbb‡ cccc' And I would like to split this string with the delimiter followed by

Solution 1:

I was having similar but slight different problem. Anyway, here are examples of three different scenarios for where to keep the deliminator.

"1、2、3".split("、") == ["1", "2", "3"]
"1、2、3".split(/(、)/g) == ["1", "、", "2", "、", "3"]
"1、2、3".split(/(?=、)/g) == ["1", "、2", "、3"]
"1、2、3".split(/(?!、)/g) == ["1、", "2、", "3"]
"1、2、3".split(/(.*?、)/g) == ["", "1、", "", "2、", "3"]

Warning: The fourth will only work to split single characters. ConnorsFan presents an alternative:

// Split a path, but keep the slashes that follow directoriesvar str = 'Animation/rawr/javascript.js';
var tokens = str.match(/[^\/]+\/?|\//g);

Solution 2:

Use (positive) lookahead so that the regular expression asserts that the special character exists, but does not actually match it:

string.split(/<br \/>(?=&#?[a-zA-Z0-9]+;)/g);

See it in action:

var string = "aaaaaa<br />&dagger; bbbb<br />&Dagger; cccc";
console.log(string.split(/<br \/>(?=&#?[a-zA-Z0-9]+;)/g));

Solution 3:

If you wrap the delimiter in parantheses it will be part of the returned array.

string.split(/(<br \/>&#?[a-zA-Z0-9]+);/g);
// returns ["aaaaaa", "<br />&dagger;", "bbbb", "<br />&Dagger;", "cccc"]

Depending on which part you want to keep change which subgroup you match

string.split(/(<br \/>)&#?[a-zA-Z0-9]+;/g);
// returns ["aaaaaa", "<br />", "bbbb", "<br />", "cccc"]

You could improve the expression by ignoring the case of letters string.split(/()&#?[a-z0-9]+;/gi);

And you can match for predefined groups like this: \d equals [0-9] and \w equals [a-zA-Z0-9_]. This means your expression could look like this.

string.split(/<br \/>(&#?[a-z\d]+;)/gi);

There is a good Regular Expression Reference on JavaScriptKit.

Solution 4:

answered it here also JavaScript Split Regular Expression keep the delimiter

use the (?=pattern) lookahead pattern in the regex example

varstring = '500x500-11*90~1+1';
string = string.replace(/(?=[$-/:-?{-~!"^_`\[\]])/gi, ",");
string = string.split(",");

this will give you the following result.

[ '500x500', '-11', '*90', '~1', '+1' ]

Can also be directly split

string = string.split(/(?=[$-/:-?{-~!"^_`\[\]])/gi);

giving the same result

[ '500x500', '-11', '*90', '~1', '+1' ]

Solution 5:

I made a modification to jichi's answer, and put it in a function which also supports multiple letters.

String.prototype.splitAndKeep = function(separator, method='seperate'){
    var str = this;
    if(method == 'seperate'){
        str = str.split(newRegExp(`(${separator})`, 'g'));
    }elseif(method == 'infront'){
        str = str.split(newRegExp(`(?=${separator})`, 'g'));
    }elseif(method == 'behind'){
        str = str.split(newRegExp(`(.*?${separator})`, 'g'));
        str = str.filter(function(el){return el !== "";});
    }
    return str;
};

jichi's answers 3rd method would not work in this function, so I took the 4th method, and removed the empty spaces to get the same result.

edit: second method which excepts an array to split char1 or char2

String.prototype.splitAndKeep = function(separator, method='seperate'){
    var str = this;
    functionsplitAndKeep(str, separator, method='seperate'){
        if(method == 'seperate'){
            str = str.split(newRegExp(`(${separator})`, 'g'));
        }elseif(method == 'infront'){
            str = str.split(newRegExp(`(?=${separator})`, 'g'));
        }elseif(method == 'behind'){
            str = str.split(newRegExp(`(.*?${separator})`, 'g'));
            str = str.filter(function(el){return el !== "";});
        }
        return str;
    }
    if(Array.isArray(separator)){
        var parts = splitAndKeep(str, separator[0], method);
        for(var i = 1; i < separator.length; i++){
            var partsTemp = parts;
            parts = [];
            for(var p = 0; p < partsTemp.length; p++){
                parts = parts.concat(splitAndKeep(partsTemp[p], separator[i], method));
            }
        }
        return parts;
    }else{
        returnsplitAndKeep(str, separator, method);
    }
};

usage:

str = "first1-second2-third3-last";

str.splitAndKeep(["1", "2", "3"]) == ["first", "1", "-second", "2", "-third", "3", "-last"];

str.splitAndKeep("-") == ["first1", "-", "second2", "-", "third3", "-", "last"];

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