From CRM REST Builder:
Xrm.WebApi.online.retrieveMultipleRecords("account", null).then(
function success(results) {
for (var i = 0; i < results.entities.length; i++) {
var accountid = results.entities[i]["accountid"];
}
},
function(error) {
Xrm.Utility.alertDialog(error.message);
}
);
