JavaScript, detecting repeated characters

Question

JavaScript, detecting repeated characters

I need to create a script that checks an input box (password) for the occurrence of the same character appearing twice. This script should work alongside existing regex validation. I believe I will need to use a loop to check if any character appears twice, but I am unsure about the conditions for this function. If anyone has suggestions on how to accomplish this, it would be greatly appreciated. For example: "ABad12" should pass, while "AbAc12" should return false. Thank you in advance.

function checkForm(form)


{

 var re = /^\w{6,10}$/;

  if(!re.test(form.pwd1.value)) {
  alert("Error: Password must be between 6-10 characters!");
  form.inputfield.focus();
  return false;
  }


}

Above is an example of the script I want to combine with additional regex validations.

javascript validation loops for-loop character

Answer 1

Answer №1

If I were to tackle this task, here's how I'd go about it:

let testString = "ABad12",
    isValid = testString.split("").filter(function(char, index, array) {
        return array.indexOf(char) !== index;
    }).length === 0;

if (!isValid) {
    // ...
}

It's worth noting that the filter() method may not be supported in older browsers, so be sure to check the browser compatibility page beforehand.

Answer 2

If I were to tackle this task, here's how I'd go about it:

let testString = "ABad12",
    isValid = testString.split("").filter(function(char, index, array) {
        return array.indexOf(char) !== index;
    }).length === 0;

if (!isValid) {
    // ...
}

It's worth noting that the filter() method may not be supported in older browsers, so be sure to check the browser compatibility page beforehand.

Answer 3

Answer №2

Forget about using a for loop, all you need is a basic regex pattern:

(\w)\1+

var checkRegex=/(\w)\1+/;
checkRegex.test("aa") -> will result in true;
checkRegex.test("ab") -> will result in false;

Answer 4

Forget about using a for loop, all you need is a basic regex pattern:

(\w)\1+

var checkRegex=/(\w)\1+/;
checkRegex.test("aa") -> will result in true;
checkRegex.test("ab") -> will result in false;

Answer 5

Answer №3

Here is a straightforward piece of code written in pure JavaScript, without using regular expressions:

function checkForDuplicates(s) {
  var index;
  for(index = 0; index < s.length - 1; index++) {
    if(s.indexOf(s.substring(index, index + 1), index + 1) >= 0) {
      return false;
    }
  }
  return true;
}

This function scans the string sequentially and verifies if any character is repeated later within the string.

Incorporating this code into your project can enable you to provide customized error messages. Instead of simply returning false, consider calling an error handling function to display a specific message such as

'Error: character “' + s.charAt(index) + '” appears more than once.'

Answer 6

Here is a straightforward piece of code written in pure JavaScript, without using regular expressions:

function checkForDuplicates(s) {
  var index;
  for(index = 0; index < s.length - 1; index++) {
    if(s.indexOf(s.substring(index, index + 1), index + 1) >= 0) {
      return false;
    }
  }
  return true;
}

This function scans the string sequentially and verifies if any character is repeated later within the string.

Incorporating this code into your project can enable you to provide customized error messages. Instead of simply returning false, consider calling an error handling function to display a specific message such as

'Error: character “' + s.charAt(index) + '” appears more than once.'

JavaScript, detecting repeated characters

Answer №1

Answer №2

Answer №3

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