OData

1. include jquery, and jso library

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To hide a field use

Xrm.Page.getControl("attributename").setVisible(true);

if it doesn't work then use

document.getElementById("attributename_c").style.display = "inline/none";
document.getElementById("attributename_d").style.display= "inline/none";

use inline to show, and none to hide the field
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To change the required field level use

 Xrm.Page.getAttribute("to").setRequiredLevel("required");

valid values are none, required and recommended

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function UpdateActivity()
{

    var CRMObject = new Object();
          CRMObject.proprtyname = value;
          updateRecord(guid, CRMObject, "EntityNameSet", null, null)
}