JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://ajax.microsoft.com/ajax/jquery.validate/1.7/jquery.validate.js"></script>
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/ui-lightness/jquery-ui.css">
Enter yes or no: <input type='text' />

JavaScript

$('input').blur(function() {
    var val = this.value.toLowerCase();
    if(val != "yes" && val != "no") {
        this.value = '';
        alert( "'Yes' or 'No' is required. \n Please try again.");
    }
})
    .keypress(function() {
        var val = this.value.toLowerCase();
        if(val != "yes" && val != "no") {
            this.value = '';
        }
    })
    .keyup(function() {
        var val = this.value.toLowerCase();
        if("yes".indexOf(val) != 0 &&
           "no".indexOf(val) != 0) {
               this.value = this.value.substr(0,this.value.length - 1);
           }
    });