helper.js

({
	rebuildRecord : function(record, describe) {

		let testobj = {
		  apiName: "Account",
		  fields : {
		    Name : {
		      displayValue:null,
		      value: "Burlington Textiles Corp of America"
		    }
		  },
		  id : "001B000000RTuZ2IAL"
		};

		//I can do this
		testobj.newField = "works fine";
		console.log(testobj.newField); // "works fine"

		//This works
		testobj.fields.Name.addedData = "Fine";
		console.log(testobj.fields.Name.addedData);

		//This works
		testobj.fields['Name'].addedData = "Fine, too";
		console.log(testobj.fields['Name'].addedData);



		//let's prove that it's not object.assign related
		let testobj2 = Object.assign({}, testobj, {});

		//This works
		testobj2.fields.Name.moreData = "Still Fine after Clone";
		console.log(testobj2.fields.Name.moreData);



		//now with a clone of data passed in to the function instead of created locally
		let testobj3 = Object.assign({}, record, {});

		testobj3.newField = "works fine";
		console.log(testobj3.newField); // "works fine"

		//This works
		testobj3.fields.Name.addedData = "Fails";
		console.log(testobj3.fields.Name.addedData); //undefined

		//This doesn't work
		testobj3.fields['Name'].addedData = "Fails, too";
		console.log(testobj3.fields['Name'].addedData); //undefined

		return testobj;
	}
})