In this blog i am going to show how you can retrieve a lookup value and set it.

for e.g if you need to set one contact which in a regarding field on an activity to another contact field.

use the below simple JavaScript:

function yourFunctionName()

var lookup = new Array();  // create a new array
lookup = Xrm.Page.getAttribute("regardingobjectid").getValue(); // get field value
if (lookup != null) 
{
var name = lookup[0].name; // get the name of the record
var id = lookup[0].id; // get the  id of the record
var entityType = lookup[0].entityType; // get the entitytype
now we have retrieved all information that we needed ; its time we set it 🙂

if (entityType == "contact")
{ // ignore this step if its not a multilookup field
var value = new Array(); //create a new object array
value[0] = new Object();
value[0].id = id; // set ID to ID
value[0].name = name; //set name to name
value[0].entityType = "contact"; //optional
Xrm.Page.getAttribute("from").setValue(value); //set the value.
}
}
}
}

Call this function on Onload of the required form.

hope it helps !!

cheers