If you need implement of HMAC-SHA1 on javascript, use crypto-js lib.
<script type="text/javascript" src="http://crypto-js.googlecode.com/files/2.3.0-crypto-sha1-hmac.js"></script>
<script type="text/javascript">
var hmac = Crypto.HMAC(Crypto.SHA1, "Message", "Secret Passphrase");
var hmacBytes = Crypto.HMAC(Crypto.SHA1, "Message", "Secret Passphrase", { asBytes: true });
var hmacString = Crypto.HMAC(Crypto.SHA1, "Message", "Secret Passphrase", { asString: true });
</script>