contrasts in regex special characters: .net versus javascript

Here is my current javascript implementation:

EscapeForRegex = function(input) {
        var specials = ["[", "\\", "^", "$", ".", "|", "?", "*", "+", "(", ")", "{", "}"]
        for (var k in specials) {
            var special = specials[k];
            input = input.replace(new window.RegExp("\\" + special, "g"), "\\" + special);
        }
        return input;
    };

But when I compare my code to the information provided at http://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex.escape.aspx, I noticed two differences.

  1. I included the character ], which the reference page does not. Do we really need to include ]? (I understand it's in a different language, but my code is in javascript)

  2. I missed out the character #. Is the # symbol considered special in javascript regex?

Answer №1

1) I have added ] but the page does not show it. Is it true that we do not need to add the ]? (I am not questioning the page, but since I am using JavaScript and not c#/vb..)

] only needs to be escaped inside a character set. The list is also missing the -, which sometimes needs to be escaped inside character sets. For example, to create a character set containing the characters space, dash, and the letter A, you would need to escape the - like this: /[ \-A]/ or move the dash to the side: /[- A]/.

Out of the characters listed above, only ], -, ^, and \\ ever need to be escaped in character sets. The ^ only needs to be escaped inside a character set if it is within the character set and at the beginning.

If you want to include the regular expression text in the literal form, /.../ instead of new RegExp("..."), you also need to escape line terminator characters: codepoint U+000A, U+000D, U+2028, U+2029, and the / character when outside a character set.

2) I forgot to include #. Is the # symbol special in JavaScript regex?

No, # is not special in JavaScript.

Answer №2

Just a heads up, you can simplify your function like this:

function RegexEscape(str){
    return str.replace(/[(-.]|[$?[\]\\^|{}]/g, '\\$&');
}

This updated version excludes #, but now includes ] and -, as noted by Mike Samuel.

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