Radio Button Event Handler

var rad = document.myForm.myRadios
var prev = null
for (var i = 0 i < rad.length i++) {
    rad[i].addEventListener('change', function() {
        (prev) ? console.log(prev.value): null
        if (this !== prev) {
            prev = this
        }
        console.log(this.value)
    })
}

<form name="myForm">
  <input type="radio" name="myRadios"  value="1" />
  <input type="radio" name="myRadios"  value="2" />
</form>