A CodePen by Artur Pokusin. Code Unlock - A simple unlock UI element that I'm working on for a side project. It validates to "1234"

index.html

<div>
  <h3>enter code</h3>
  <form class="code_input">
    <input type="text" maxlength="1" placeholder="#" autofocus></input>
    <input type="text" maxlength="1" placeholder="#"></input>
    <input type="text" maxlength="1" placeholder="#"></input>
    <input type="text" maxlength="1" placeholder="#"></input>
  </form>

  <ul class="hint">
    <li>Valid Code: <strong>1234</strong></li>
  </ul>
</div>

script.js

// Form element
var form = $(".code_input");
var formInputs = $("input");

var validCode = "1234";

$(formInputs).autotab_magic();

var inputCode = function() {
  var code = [];            
  $(formInputs).each(function(){
    code.push($(this).val());
  });
  return code.join("");
};

var validateCode = function() {
  var c = inputCode();
  if ( c === validCode ) {
    $(form).removeClass("error").addClass("success");
    $(".hint").fadeOut();
    return false;
  } else if ( c.length === 4 ) {
    $(".hint").fadeIn();
  } else {
    $(form).addClass("error").removeClass("success");
    return false;
  }
}

var clearInputs = function() {
  $("input:first-child").focus();
  $(formInputs).val('');
  $(form).removeClass();
};

$(formInputs).keyup(function() {
  if (event.keyCode == 8 || event.keyCode == 46) {
    clearInputs();
    return false;
  } else {
    validateCode();
  }
});

$(formInputs).click(function() {
  validateCode();
  clearInputs();
});

style.css

* {
  box-sizing: border-box;
  text-rendering: optimizeLegibility;
  margin: 0;
  padding: 0;
}

body {
  font-family: "Source Sans Pro", sans-serif;
  text-align: center;
  padding: 1em;
  color: #ccc;
  font-weight: 200;
}

div {
  width: 200px;
  text-align: center;
  margin: 0 auto;
  position: absolute;
  top: 50%;
  left: 50%;
  margin-left: -100px;
  margin-top: -70px;
}

h3 {
  font-weight: 100;
  font-size: 28px;
  color: #ccc;
  line-height: 36px;
  margin-bottom: 1em;
}

form {
  width: auto;
}

form.success input {
  color: #8CE62C;
  border-color: #8CE62C;
}

input {
  font-family: "Source Sans Pro", sans-serif;
  font-weight: 200;
  width: 40px;
  height: 50px;
  border: 1px solid #CCCCCC;
  display: block;
  float: left;
  margin-right: 10px;
  outline: 0;
  font-size: 28px;
  color: #ccc;
  line-height: 40px;
  text-align: center;
  cursor: pointer;
}
input:hover {
  color: #9B9B9B;
}

input:focus {
  color: #0091FF;
  border-color: #0091FF;
 
}

.hint {
  display: none;
}

ul {
  padding-top: 2em;
  clear: both;
}


ul li {
  list-style-type: none;
}

strong {
  color: #777;
  font-weight: 200;
}