Then request the endpoint on Event registration page with code below and populate the form from retrieved result:
var req = new XMLHttpRequest();
req.open("GET", Url + "/_odata/openContacts", true);
req.setRequestHeader("Accept", "application/json");
req.setRequestHeader("Content-Type", "application/json; charset=utf-8");
req.setRequestHeader("Prefer", "odata.include-annotations=\"*\"");
req.onreadystatechange = function() {
if (this.readyState === 4) {
req.onreadystatechange = null;
if (this.status === 200) {
var results = JSON.parse(this.response);
for (var i = 0; i < results.value.length; i++) {
var firstname = results.value[i]["fullname"].split(" ")[0];
var lastname = results.value[i]["fullname"].split(" ")[1];
var email = results.value[i]["emailaddress1"];
}
} else {
console.log(this.statusText);
}
}
};
req.send();
