serializeGridData: function (postData) { 
			var value = Object.keys($.Autocomplete.selectionId)[0]; // value = "name"
			return $.extend(postData, {val: 'test'});  // val : test а нужно name:test
		},

var value = 'name';
var obj = {
value: 'test'
}
console.log(obj); //Object { value: "test" }

var object = {};
var myVar = "name";
object[myVar] = "value";

		serializeGridData: function (postData) { 
			var val = Object.keys($.Autocomplete.selectionId)[0];
			return $.extend(postData, Object.defineProperty( {}, val, { value: $.Autocomplete.selectionId[val],enumerable: true, writable: true, configurable: true  }) ); 
		},