Javascript regular expression to validate whether both () brackets are present

Question

Techies,

I'm working on kind of calculator, am not much comfortable with regex. My need is JavaScript regular expression to validate whether both ( ) brackets are present, there may be some character inside the brackets.

suggestions please

show us what have you tried, we are not here to do free work — Nikhil Savaliya, Mar 07 '18 at 07:11
Thanks Nikhil for your kind words. this is the expression I have tried var exp = /^($\d{3}$/ — Arun, Mar 07 '18 at 07:24

score 0 · Answer 1 · answered Mar 07 '18 at 07:17

0

Simple regex:

var string = '1234 + 1234 (5)';
if (string.match('\(|\)')) {
    console.log('() found')
}

answered Mar 07 '18 at 07:17

Tony Stark

330
3
12

This just checks if any bracket is present - no matter wether they are balanced or not. It is neither suited to check if correctly used brackets are present nor is it suited to check if unbalanced brackets are present. – Jan Wendland Mar 07 '18 at 07:24
Thanks Aldrin, its not working for below string var string = '1234 + 1234 (5' – Arun Mar 07 '18 at 07:25
Sorry, I overlooked that. Does it have to be regex though? – Tony Stark Mar 07 '18 at 07:50
yeah Aldrin, I need it as regex – Arun Mar 07 '18 at 07:51

SamWhan · Answer 2 · 2018-03-07T13:26:18.097

Simply matching

\(.*\)

will match if both an opening, and a closing parentheses are present. (Parentheses need to be escaped since it's a special character in regex.) .* matches anything, including an empty string.

But I assume you'd want to allow strings without any parentheses as well. This regex allows for any number of pairs of parentheses (not nested) or none at all:

^[^()]*(?:\([^()]*\)[^()]*)*$

It matches start of string ^, a string of any length not containing parentheses [^()]*. Then any number of the combination 1. Opening P(arentheses) 2. Any length string w/o P's. 3. A closing P. 4. Any length string w/o P's. (Possibly repeated any number of times.) Finally it matches end of string $.

Working example (Type an expression into the input control, and press Enter.):

var inputExpression = document.getElementById("expression");

function testExpression(){
    console.log(inputExpression.value.match(/^[^()]*(?:\([^()]*\)[^()]*)*$/) ? "Well formed" : "Unbalanced parentheses");
//    inputExpression.value = '';
}


inputExpression.addEventListener("keyup", function(event) {
    event.preventDefault();
    if (event.keyCode === 13) {
        testExpression();
    }
});

Enter an expression:<input id="expression" type="text" onBlur="testExpression()"/>

Javascript regular expression to validate whether both () brackets are present

2 Answers2