<form onsubmit="return Validate(this)" method="get" action="http://cscie12.dce.harvard.edu/echo">
<div><label for="email1">Email Address</label>:
<input type="text" size="32" name="email" id="email1"/><br/>
<input type="submit"/></div>
</form>

In head element:

<script type="text/javascript" src="example9.js"> </script>

Contents of example9.js

/* validates that the entry is formatted as an email address */
function Validate(thisForm) {
    var tocheck = thisForm.email.value;
    var re = /^[\w\._-]+@[\w\._-]+\.[a-zA-Z]{2,7}$/;
    if (!tocheck.match(re)) {
        alert("Please verify the email address format.");
        thisForm.email.focus();
        thisForm.email.style.backgroundColor = '#ff9';
        return false;
    } else {
        return true;
    }
}