Restrict Text Input Characters HTML JavaScript Tutorial
Learn to restrict one or more text fields in a form to allow only characters that you desire to be typed into them. We will remove undesirable characters in real time as the user types.
<script>
function lettersOnly(input) {
var regex = /[^a-z]/gi;
input.value = input.value.replace(regex, "");
}
</script>
<input id="firstname" placeholder="first name" onkeyup="lettersOnly(this)">
<input id="lastname" placeholder="last name" onkeyup="lettersOnly(this)">