How to detect a certain sequence of numbers in javascript?

Question

In the address registration field, I have the zip code. In this cep field, I need to make some validations:

1 - Do not allow the user to type a sequence with two alternating numbers:

EX 1: "12121212"
EX 2: "12312312"

2 - Do not allow the user to type a sequence of a given number:

EX: "111111111"

How could I do that? I couldn’t make a regex that would handle both situations.

Answer 1

I first created a function to check for duplicates in the string, which works as follows: check the string passed if the numbers contain the repetition ( using the previous reference ) for the 2 number repetition case.

Then I created one to check repeated content, where I used a reduce in the content; I took the first position and checked if all others are equal to it, if yes, returns true...

In the end I check the negation of existing duplicates and there are all repeated ones so it is a valid string.

var str1 = "121212122";
var str2 = "111111111";
var str3 = "123456789";

var is_repetidos = function(str) {
  return /([0-9])\1+/g.test(str);
}

var todos_iguais = function(str) {

  var conteudo_separado = str.split("");

  return conteudo_separado.reduce(function(a, b) {
    return a == b;
  }, str[0]);

}

var is_valid = function(str) {
  return !(is_repetidos(str) || todos_iguais(str));
}

var dados = [str1, str2, str3];

for (var i = 0; i < dados.length; i++) {
  console.log(dados[i] + " = " + is_valid(dados[i]))
}

Answer 2

You can validate repetitions with the following expression: /([0-9]{2,3})\1/g

It will evaluate whether there are groups of 2 or 3 digits repeated, ie : 1212 or 123123

Example:

var cep = document.querySelector("input[name=cep]");


function fazRegex(){
	var reg = /([0-9]{2,3})\1/g;
  
 
  if(reg.test(cep.value))
  	document.querySelector("#resultado").innerHTML = "Errado";
  else
  	document.querySelector("#resultado").innerHTML = "Certo";
}

cep.addEventListener("keyup", fazRegex);

<input type="text" name="cep" onkeyup="fazRegex()"/>
<div id="resultado"></div>

See also on jsFindle

If you want to test the expression more deeply I strongly advise you to visit the site:

regular Expressions 101