<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script>
window.addEventListener('DOMContentLoaded', function() {
var input = document.querySelector('[name="comment"]'),
a = document.querySelector('#nhome');
input.addEventListener('input', function() {
this.value = this.value.replace(/\D/g,'');
a.textContent = +this.value < 101 ? "не верно" : "Изменить";
}, false);
a.addEventListener("click", function(event) {
if(+input.value < 101) event.preventDefault();
}, false);
});
</script>
</head>
<body>
<input type="text" name="comment" />
<a id="nhome" href="home.html">Изменить</a>
</body>
</html>