1diff --git a/TODO.md b/TODO.md
  2index cdf5d6b..1fdf193 100644
  3--- a/TODO.md
  4+++ b/TODO.md
  5@@ -20,9 +20,6 @@ We could give each function a type-array that matches the arguments, and could b
  6 ### Fix documentation regular expression, it is butchering URLs.
  7 
  8 
  9-### ISERROR, ISNA need to be called inside a try-catch-block inside the Parser or Sheet.
 10-
 11-
 12 ### Cells/Sheet/Parser should be able to parse raw errors in the format `#N/A`
 13 All errors should be able to be input/thrown in this way.
 14 
 15diff --git a/src/Formulas/AllFormulas.ts b/src/Formulas/AllFormulas.ts
 16index 0930dae..b67327c 100644
 17--- a/src/Formulas/AllFormulas.ts
 18+++ b/src/Formulas/AllFormulas.ts
 19@@ -268,7 +268,8 @@ const __TRY_CATCH_FORMULAS : Object = {
 20   "ERRORTYPE": ERRORTYPE,
 21   "ISERR": ISERR,
 22   "ISERROR": ISERROR,
 23-  "ISNA": ISNA
 24+  "ISNA": ISNA,
 25+  "IFERROR": IFERROR
 26 };
 27 
 28 export {
 29diff --git a/src/Formulas/Info.ts b/src/Formulas/Info.ts
 30index 747c08a..19e557d 100644
 31--- a/src/Formulas/Info.ts
 32+++ b/src/Formulas/Info.ts
 33@@ -19,7 +19,7 @@ import {Filter} from "../Utilities/Filter";
 34  * @constructor
 35  */
 36 let NA = function () {
 37-  ArgsChecker.checkLength(arguments, 1, "NA");
 38+  ArgsChecker.checkLength(arguments, 0, "NA");
 39   throw new NAError("NA Error thrown.");
 40 };
 41 
 42@@ -257,7 +257,7 @@ let ISERROR = function (value) {
 43   if (value instanceof Cell) {
 44     return value.hasError();
 45   }
 46-  return value instanceof Error;
 47+  return (value instanceof Error);
 48 };
 49 
 50 
 51@@ -294,14 +294,19 @@ let ISNA = function (value) {
 52  * @param valueIfError - [OPTIONAL] - Value to return if no error is present in the first argument.
 53  * @returns {any}
 54  * @constructor
 55- * TODO: This formula needs to be called from inside a try-catch-block in the Sheet/Parser, like ERROR.TYPE.
 56  */
 57 let IFERROR = function (value, valueIfError?) {
 58   ArgsChecker.checkLengthWithin(arguments, 1, 2, "IFERROR");
 59-  if (value instanceof Cell && valueIfError === undefined) {
 60-    return ISERROR(value) ? new Cell(value.getId()) : value;
 61+  if (value instanceof Cell) {
 62+    if (value.hasError()) {
 63+      return;
 64+    }
 65+    return value;
 66+  }
 67+  if (!ISERROR(value)) {
 68+    return value;
 69   }
 70-  return ISERROR(value) ? valueIfError : value;
 71+  return;
 72 };
 73 
 74 
 75diff --git a/src/Sheet.ts b/src/Sheet.ts
 76index e99bf4d..88935c9 100644
 77--- a/src/Sheet.ts
 78+++ b/src/Sheet.ts
 79@@ -217,14 +217,6 @@ let Sheet = (function () {
 80       return value instanceof Function;
 81     },
 82 
 83-    isNull: function (value) {
 84-      return value === null;
 85-    },
 86-
 87-    isSet: function (value) {
 88-      return !utils.isNull(value);
 89-    },
 90-
 91     toNum: function (chr) {
 92       chr = utils.clearFormula(chr);
 93       let base = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', i, j, result = 0;
 94diff --git a/tests/Formulas/InfoTest.ts b/tests/Formulas/InfoTest.ts
 95index 9ba556d..0d9dd65 100644
 96--- a/tests/Formulas/InfoTest.ts
 97+++ b/tests/Formulas/InfoTest.ts
 98@@ -230,7 +230,8 @@ test("ISNA", function(){
 99 test("IFERROR", function(){
100   let errorCell = new Cell("A1");
101   errorCell.setError(new NAError("err"));
102-  assertEquals(IFERROR(errorCell, 10), 10);
103+  assertEquals(IFERROR(errorCell, 10), undefined);
104+  assertEquals(IFERROR(new NAError("err")), undefined);
105   assertEquals(IFERROR(10), 10);
106   assertEquals(IFERROR(Cell.BuildFrom("A1", 10), "abc"), Cell.BuildFrom("A1", 10));
107   assertEquals(IFERROR(new Cell("A1")), new Cell("A1"));
108diff --git a/tests/SheetFormulaTest.ts b/tests/SheetFormulaTest.ts
109index c3cd7aa..4249f09 100644
110--- a/tests/SheetFormulaTest.ts
111+++ b/tests/SheetFormulaTest.ts
112@@ -884,6 +884,7 @@ test("Sheet ISNA", function(){
113 
114 test("Sheet IFERROR", function(){
115   assertFormulaEquals('=IFERROR(10)', 10);
116+  assertFormulaEquals('=IFERROR(NA())', undefined);
117 });
118 
119 test("Sheet TYPE", function(){