<!-- see https://github.com/estelle/input-masking/ for a detailed explanation--><ul>
  <li>
    <label for="expiration">Credit Card Expiration Month</label>
    <input id="expiration" type="tel" placeholder="MM/YY" class="masked" pattern="(1[0-2]|0[1-9])\/\d\d" data-valid-example="11/18" title="2-digit month and 2-digit year">
  </li>

<li>
  <label for="zip">Zip Code</label>
  <input id="zip" type="tel" name="zipcode" placeholder="XXXXX" pattern="\d{5}" class="masked" title="5-digit zip code">
</li>
<li>
  <label for="zipca">Canadian Zip Code</label>
  <input id="zipca" type="text" name="zipcodeca" placeholder="XXX XXX" pattern="\w\d\w \d\w\d" class="masked" data-charset="_X_ X_X" title="6-character alphanumeric zip code in the format of A1A 1A1">
</li>
<li>
  <label for="tel">Telephone</label>
  <input id="tel" type="tel" name="phone" placeholder="(XXX) XXX-XXXX" pattern="\(\d{3}\) \d{3}\-\d{4}" class="masked" title="10-digit number">
</li>
<li>
  <label for="cc">Credit Card Number</label>
  <input id="cc" type="tel" name="ccnumber" placeholder="XXXX XXXX XXXX XXXX" pattern="\d{4} \d{4} \d{4} \d{4}" class="masked" title="16-digit number">
</li>
</ul>

/* Libary CSS */
.shell {
  position: relative;
  line-height: 1;
  span {
  position: absolute;
  left: 3px;
  top: 1px;
  color: red;
  pointer-events: none;
  z-index: -1;
    i { /* any of these 3 will work */
        color: transparent;
        opacity: 0;
        visibility: hidden;
    }
  }
}

input.masked,
.shell span {
  font-size: 16px;
  font-family: monospace;
  padding-right: 10px;
  background-color: transparent;
  text-transform: uppercase;
}

/* Look and feel (not lib specific) */

li {
  line-height: 2;
  font-family: helvetica;
  list-style-type: none;
  border-bottom: 1px solid #ccc;
}
label { 
  display: inline-block;
  width: 14em;
}
input {
  border: none;
}

var masking = {

  // User defined Values
  //maskedInputs : document.getElementsByClassName('masked'), // add with IE 8's death
  maskedInputs : document.querySelectorAll('.masked'), // kill with IE 8's death
  maskedNumber : 'XdDmMyY9',
  maskedLetter : '_',

  init: function () {
    masking.setUpMasks(masking.maskedInputs);
    masking.maskedInputs = document.querySelectorAll('.masked'); // Repopulating. Needed b/c static node list was created above.
    masking.activateMasking(masking.maskedInputs);
  },

  setUpMasks: function (inputs) {
    var i, l = inputs.length;

    for(i = 0; i < l; i++) {
      masking.createShell(inputs[i]);
    }
  },
  
  // replaces each masked input with a shall containing the input and it's mask.
  createShell : function (input) {
    var text = '', 
        placeholder = input.getAttribute('placeholder');

    input.setAttribute('maxlength', placeholder.length);
    input.setAttribute('data-placeholder', placeholder);
    input.removeAttribute('placeholder');

    text = '<span class="shell">' +
      '<span aria-hidden="true" id="' + input.id + 
      'Mask"><i></i>' + placeholder + '</span>' + 
      input.outerHTML +
      '</span>';

    input.outerHTML = text;
  },

  setValueOfMask : function (e) {
    var value = e.target.value,
        placeholder = e.target.getAttribute('data-placeholder');

    return "<i>" + value + "</i>" + placeholder.substr(value.length);
  },
  
  // add event listeners
  activateMasking : function (inputs) {
    var i, l;

    for (i = 0, l = inputs.length; i < l; i++) {
      if (masking.maskedInputs[i].addEventListener) { // remove "if" after death of IE 8
        masking.maskedInputs[i].addEventListener('keyup', function(e) {
          masking.handleValueChange(e);
        }, false); 
      } else if (masking.maskedInputs[i].attachEvent) { // For IE 8
          masking.maskedInputs[i].attachEvent("onkeyup", function(e) {
          e.target = e.srcElement; 
          masking.handleValueChange(e);
        });
      }
    }
  },
  
  handleValueChange : function (e) {
    var id = e.target.getAttribute('id');
        
    switch (e.keyCode) { // allows navigating thru input
      case 20: // caplocks
      case 17: // control
      case 18: // option
      case 16: // shift
      case 37: // arrow keys
      case 38:
      case 39:
      case 40:
      case  9: // tab (let blur handle tab)
        return;
      }

    document.getElementById(id).value = masking.handleCurrentValue(e);
    document.getElementById(id + 'Mask').innerHTML = masking.setValueOfMask(e);

  },

  handleCurrentValue : function (e) {
    var isCharsetPresent = e.target.getAttribute('data-charset'), 
        placeholder = isCharsetPresent || e.target.getAttribute('data-placeholder'),
        value = e.target.value, l = placeholder.length, newValue = '', 
        i, j, isInt, isLetter, strippedValue;

    // strip special characters
    strippedValue = isCharsetPresent ? value.replace(/\W/g, "") : value.replace(/\D/g, "");

    for (i = 0, j = 0; i < l; i++) {
        var x = 
        isInt = !isNaN(parseInt(strippedValue[j]));
        isLetter = strippedValue[j] ? strippedValue[j].match(/[A-Z]/i) : false;
        matchesNumber = masking.maskedNumber.indexOf(placeholder[i]) >= 0;
        matchesLetter = masking.maskedLetter.indexOf(placeholder[i]) >= 0;

        if ((matchesNumber && isInt) || (isCharsetPresent && matchesLetter && isLetter)) {

                newValue += strippedValue[j++];

          } else if ((!isCharsetPresent && !isInt && matchesNumber) || (isCharsetPresent && ((matchesLetter && !isLetter) || (matchesNumber && !isInt)))) {
                // masking.errorOnKeyEntry(); // write your own error handling function
                return newValue; 

        } else {
            newValue += placeholder[i];
        } 
        // break if no characters left and the pattern is non-special character
        if (strippedValue[j] == undefined) { 
          break;
        }
    }
    if (e.target.getAttribute('data-valid-example')) {
      return masking.validateProgress(e, newValue);
    }
    return newValue;
  },

  validateProgress : function (e, value) {
    var validExample = e.target.getAttribute('data-valid-example'),
        pattern = new RegExp(e.target.getAttribute('pattern')),
        placeholder = e.target.getAttribute('data-placeholder'),
        l = value.length, testValue = '';

    //convert to months
    if (l == 1 && placeholder.toUpperCase().substr(0,2) == 'MM') {
      if(value > 1 && value < 10) {
        value = '0' + value;
      }
      return value;
    }
    // test the value, removing the last character, until what you have is a submatch
    for ( i = l; i >= 0; i--) {
      testValue = value + validExample.substr(value.length);
      if (pattern.test(testValue)) {
        return value;
      } else {
        value = value.substr(0, value.length-1);
      }
    }
  
    return value;
  },

  errorOnKeyEntry : function () {
    // Write your own error handling
  }
}

masking.init();