how to replace undefined with a empty string
As per this answer I believe what you want is
doc.text(50, 190, $scope.currentItem.JobOriginalBudget || " ")
undefined is a primitive value. Instead of comparing against the identifier undefined, you're comparing against the 9-character string "undefined".
Simply remove the quotes:
if ($scope.currentItem.JobOriginalBudget == undefined)Or compare against the typeof result, which is a string:
if (typeof $scope.currentItem.JobOriginalBudget == "undefined")
simply remove the "== 'undefined'"
if (!$scope.currentItem.JobOriginalBudget) { doc.text(50, 190, " ");}