Using regular expressions to identify the presence of "&", parentheses, and consecutive letters in a string

Question

Using regular expressions to identify the presence of "&", parentheses, and consecutive letters in a string

I specialize in working with JavaScript and I have a need to verify if my text contains certain characters. Specifically, I want to check for the presence of parentheses (), ampersands (&), and repeating letters within the text. Here are some examples:

test - contains multiple instances of 't'

tes&t - contains '&'

test(test) - contains '(' and ')', multiple 't's, and two occurrences of 'e'

test&(test - contains '&', '(', multiple 't's, and 'e's

test&(&t - contains multiple 't's, multiple '&'s, and '('

tesra - does not match any patterns mentioned above

I've already written the following code snippet:

if ((/(\w+)(?=\1)/g).test(str)) alert('multiple signs')

However, this code only detects consecutive duplicate signs, so 'teest' would be detected but 'test' wouldn't. Can anyone provide assistance with this? RegEx features have always been challenging for me :( This task can probably be tackled using two separate RegEx expressions.

Thank you in advance

javascript regex

Answer 1

Answer №1

To improve your lookahead, simply add a .*.

(\w)(?=.*\1)|[()&]

Take a look at it on regexr by clicking here

I also included a character class in the alternation to cover the letters you requested: ()&

If you prefer only ASCII letters instead of \w, use a character class

([a-zA-Z])(?=.*\1)|[()&]

Answer 2

To improve your lookahead, simply add a .*.

(\w)(?=.*\1)|[()&]

Take a look at it on regexr by clicking here

I also included a character class in the alternation to cover the letters you requested: ()&

If you prefer only ASCII letters instead of \w, use a character class

([a-zA-Z])(?=.*\1)|[()&]

Answer 3

Answer №2

Here is a potential solution, which may not be the most efficient as it is not anchored:

(?:[&()]|(\w)[^\1]*\1)

Alternatively, you could iterate over the characters, examine and tally them:

function checkForMultipleCharacters(str, extra) {
    var characters = {};
    for(var i = 0; i < str.length; i++) {
        var character = str.charAt(i);
        if(character in characters || character in extra) {
            return true;
        }
        else {
            characters[character] = 1;
        }
    }
    return false;
}

var hasMultipleChars = checkForMultipleCharacters(str, {'(': 1, ')': 1, '&': 1});

(Admittedly, the function name may not be the most fitting)

Answer 4

Here is a potential solution, which may not be the most efficient as it is not anchored:

(?:[&()]|(\w)[^\1]*\1)

Alternatively, you could iterate over the characters, examine and tally them:

function checkForMultipleCharacters(str, extra) {
    var characters = {};
    for(var i = 0; i < str.length; i++) {
        var character = str.charAt(i);
        if(character in characters || character in extra) {
            return true;
        }
        else {
            characters[character] = 1;
        }
    }
    return false;
}

var hasMultipleChars = checkForMultipleCharacters(str, {'(': 1, ')': 1, '&': 1});

(Admittedly, the function name may not be the most fitting)

Using regular expressions to identify the presence of "&", parentheses, and consecutive letters in a string

Answer №1

Answer №2

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