Remove zero-width space characters from a JavaScript string

I take user-input (JS code) and execute (process) them in realtime to show some output.

Sometimes the code has those zero-width spaces; it's really weird. I don't know how the users are inputting that. Example: "(​$".length === 3

I need to be able to remove that character from my code in JS. How do I do so? or maybe there's some other way to execute that JS code so that the browser doesn't take the zero-width space characters into account?

Unicode has the following zero-width characters:

• U+200B zero width space
• U+200C zero width non-joiner Unicode code point
• U+200D zero width joiner Unicode code point
• U+FEFF zero width no-break space Unicode code point

To remove them from a string in JavaScript, you can use a simple regular expression:

var userInput = 'a\u200Bb\u200Cc\u200Dd\uFEFFe';
console.log(userInput.length); // 9
var result = userInput.replace(/[\u200B-\u200D\uFEFF]/g, '');
console.log(result.length); // 5

Note that there are many more symbols that may not be visible. Some of ASCII’s control characters, for example.

I had a problem some invisible characters were corrupting my JSON and causing Unexpected Token ILLEGAL exception which was crashing my site.

Here is my solution using RegExp variable:

    var re = new RegExp("\u2028|\u2029");
    var result = text.replace(re, '');

More about Javascript and zero width spaces you can find here: Zero Width Spaces

str.replace(/\u200B/g,'');

200B is the hexadecimal of the zero width space 8203. replace this with empty string to remove this

[].filter.call( str, function( c ) {
    return c.charCodeAt( 0 ) !== 8203;
} );

Filter each character to remove the 8203 char code (zero-width space unicode number).

If you are trying to do this in JavaScript, try this regex.

/([\u200B]+|[\u200C]+|[\u200D]+|[\u200E]+|[\u200F]+|[\uFEFF]+)/g

submit.onclick = evt => {
  const stringToTrim = stringValue.value;
  zeroWidthTrim(stringToTrim);
}

/**
 * Given a string, when it has zero-width spaces in it, then remove them
 *
 * @param {String} stringToTrim The string to be trimmed of unicode spaces
 *
 * @return the trimmed string
 *
 * Regex for zero-width space Unicode characters.
 *
 * U+200B zero-width space.
 * U+200C zero-width non-joiner.
 * U+200D zero-width joiner.
 * U+200E left-to-right mark.
 * U+200F right-to-left mark.
 * U+FEFF zero-width non-breaking space.
 */
function zeroWidthTrim(stringToTrim) {
  const ZERO_WIDTH_SPACES_REGEX = /([\u200B]+|[\u200C]+|[\u200D]+|[\u200E]+|[\u200F]+|[\uFEFF]+)/g;
  console.log('stringToTrim = ' + stringToTrim);
  const trimmedString = stringToTrim.replace(ZERO_WIDTH_SPACES_REGEX, '');
  console.log('trimmedString = ' + trimmedString);
  return trimmedString;
};

<form runat="server">
  <input name="stringValue" id="stringValue" type="text" placeholder="enter your string" value="[&#x200b;&#x200c;]" />
  <input type="button" value="remove zero-width characters" id="submit" />
</form>

(Once you have run the above code snippet, paste the stringToTrim value and the trimmedString value into the regex101 test window and you will see that the Unicode character has gone from the trimmedString value.)