Create Notes record with Attachment for Contact Entity

var note = {};

note.subject = "Notes Subject";

note.notetext = "Notes Text";

note.filename = "FileName.txt";

note.documentbody = "Base64String";

note["objectid_contact@odata.bind"] = "/contacts(00000000-0000-0000-000000000000)";

Xrm.WebApi.createRecord("annotation", note).then(

function success(result) {

alert("Success");

},

function(error) {

alert(error.message);

});

Note:-

1. While setting object ID or regrading lookup we have to specify entity name with field schema name

for e.g. objectid_account@odata.bind

2. documentbody value should be converted to Base64String