A little misunderstanding about about data structure here, the data array is |message.extendedDisplay.records|
And I think it's OK to concat all into single string and show at once, since we don't have any references.

var msg = "";
for (var i = 0; i < message.extendedDisplay.records.length; i++) {
  msg += message.extendedDisplay.records[i].content + " ";
}