A Pen by Secret Sam.

An-Anonymous-Pen.markdown

An Anonymous Pen

A Pen by Captain Anonymous on CodePen.

License.

index.html

<div class="input_container">
  <input type="text" id="1234" maxlength="18" />
</div>

script.js

$("input").keyup(function(){
  if($(this).val().length>=18){
    $('#1234').addClass('lololo');
  }else{
    $("#1234").removeClass('lololo');
  }
});

style.css

.input_container{
  position:relative;
  display: inline-block;
  height:25px;
}
.lololo {color: gray;}