Auto Completar CEP

CEP

input type="text" style='width:200px' name="cep" id="cep" maxlength="9" onkeypress="return txtBoxFormat(this, '99999-999', event);"
a href="javascript: funcaowebservicecep();"
completar endereço


//JAVASCRIPT
function getHTTPObject() {

var xmlhttp;
/*@cc_on
@if (@_jscript_version >= 5)
try {
xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
} catch (E) {
xmlhttp = false;
}
}
@else
xmlhttp = false;
@end @*/
if (!xmlhttp && typeof XMLHttpRequest != 'undefined') {
try {
xmlhttp = new XMLHttpRequest();
} catch (e) {
xmlhttp = false;
}
}
return xmlhttp;
}

var http = getHTTPObject();

function funcaowebservicecep(){
http.open("GET", '../contato/buscarendereco.php?cep='+document.getElementById("cep").value, true);
http.onreadystatechange = handleHttpResponse;
http.send(null);

var arr; //array com os dados retornados

function handleHttpResponse(){
if (http.readyState == 4){
var response = http.responseText;
eval("var arr = "+response); //cria objeto com o resultado
document.getElementById("rua").value = arr.rua;
document.getElementById("bairro").value = arr.bairro;
document.getElementById("cidade").value = arr.cidade;
document.getElementById("uf").value = arr.uf;
}
}

}