Regular Expression for symbol characters in JavaScript

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;
    }
}

Solution

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, e.g. 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, e.g. capture group
) -- positive lookahead end

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