Regular Expression for symbol characters in JavaScript

Question

I have a quick question about the regular expression for symbols like !@#$%^&*()_+ in JavaScript. So, I am trying to implement it for the password validation, and I followed some documentation about regular expressions I found online, but it did not work correctly only for symbols (it worked for numbers and alphabet characters)

The function below is the sample code of what I used on my web application. When I type a password on the web application, this function always returns false even if I put in symbols.

function valid_password(password) {
    var sym = new RegExp('[ @#$%^&_*-+=[]{}()?]+');
    if (sym.test(password)) {
        return true;
    } else {
        return false;
    }
}

Answer 1

You need to escape special characters in your regex, such as [ , ] , - . Also, for better performance avoid compiling a new regex each time you call the function, which is only needed when you want to compose a pattern based on variable input. The .test() returns true or false, eg no need for the if/else.

Here is the function fixed:

 function hasSymbol(password) { return /[ @#$%^&_*\-+=\[\]{}()\?]/.test(password); } [ 'abc', 'a@z', 'a z', '+++' ].forEach(password => { let check = hasSymbol(password); console.log(password, '=>', check); });

Output:

abc => false
a@z => true
a z => true
+++ => true

This tests for a single symbol in a password. You might want to test for at least a number of symbols. You can do that with a positive lookahead. Here is an example for at least 3 symbols:

 function hasThreeSymbols(password) { return /^(?=(?:.*?[ @#$%^&_*\-+=\[\]{}()\?]){3,})/.test(password); } [ 'abc', 'a@z', 'a z', '+++', 'a#b$c', 'a#b$c^d' ].forEach(password => { let check = hasThreeSymbols(password); console.log(password, '=>', check); });

Output:

abc => false
a@z => false
a z => false
+++ => true
a#b$c => false
a#b$c^d => true

Explanation of regex:

• ^ -- anchor at start of string
• (?= -- positive lookahead start
  • (?: -- non-capture group start
    • .*? -- non-greedy scan for:
    • [ @#$%^&_*\-+=\[\]{}()\?] -- a single symbol
  • ) -- non-capture group end
  • {3,} -- require 3+ occurrences of previous pattern, eg capture group
• ) -- positive lookahead end

To learn more about regex: https://twiki.org/cgi-bin/view/Codev/TWikiPresentation2018x10x14Regex