diff --git a/src/Fable.Cli/CHANGELOG.md b/src/Fable.Cli/CHANGELOG.md
index 0acbf9a082..509cfd15fa 100644
--- a/src/Fable.Cli/CHANGELOG.md
+++ b/src/Fable.Cli/CHANGELOG.md
@@ -9,13 +9,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
-#### All
+* [GH-3769](https://github.com/fable-compiler/Fable/pull/3769) [All] Local plugin build does not run indefinably. (by @nojaf)
+* [GH-3769](https://github.com/fable-compiler/Fable/pull/3769) [JS/TS] Types hidden by signature files should not be exported. (by @nojaf)
+* [GH-3772](https://github.com/fable-compiler/Fable/pull/3772) [JS/TS] Re-implement `DateTime.ToString` custom format handling (by @MangelMaxime)
 
-* [GH-3769](https://github.com/fable-compiler/Fable/pull/3769) Local plugin build does not run indefinably. (by @nojaf)
+    It now supports all custom format specifiers, and behave as if `CultureInfo.InvariantCulture` was used (Fable does not support Globalization).
+* [GH-3772](https://github.com/fable-compiler/Fable/pull/3772) [JS/TS] Make compilation fails if calling `DateTime` constructor with microseconds (by @MangelMaxime)
 
-#### JavaScript
+    JavaScript `Date` does not support microseconds, we need to wait for `Temporal` to be widely supported before reconsidering this.
+
+### Changed
 
-* [GH-3769](https://github.com/fable-compiler/Fable/pull/3769) Types hidden by signature files should not be exported. (by @nojaf)
+* [GH-3772](https://github.com/fable-compiler/Fable/pull/3772) [JS/TS] Split replacement for `DateTime` and `DateTimeOffset` (by @MangelMaxime)
 
 ## 4.13.0 - 2024-02-13
 
diff --git a/src/Fable.Transforms/Replacements.fs b/src/Fable.Transforms/Replacements.fs
index 0e23c6219e..5eeeabe1ad 100644
--- a/src/Fable.Transforms/Replacements.fs
+++ b/src/Fable.Transforms/Replacements.fs
@@ -2840,15 +2840,8 @@ let ignoreFormatProvider meth args =
     | "TryParse", input :: _culture :: defVal :: _ -> [ input; defVal ]
     | _ -> args
 
-let dates (com: ICompiler) (ctx: Context) r t (i: CallInfo) (thisArg: Expr option) (args: Expr list) =
-    let getTime (e: Expr) =
-        Helper.InstanceCall(e, "getTime", t, [])
-
-    let moduleName =
-        if i.DeclaringEntityFullName = Types.datetime then
-            "Date"
-        else
-            "DateOffset"
+let dateTime (com: ICompiler) (ctx: Context) r t (i: CallInfo) (thisArg: Expr option) (args: Expr list) =
+    let moduleName = "Date"
 
     match i.CompiledName with
     | ".ctor" ->
@@ -2857,9 +2850,6 @@ let dates (com: ICompiler) (ctx: Context) r t (i: CallInfo) (thisArg: Expr optio
         | ExprType(Number(Int64, _)) :: _ ->
             Helper.LibCall(com, moduleName, "fromTicks", t, args, i.SignatureArgTypes, ?loc = r)
             |> Some
-        | ExprType(DeclaredType(e, [])) :: _ when e.FullName = Types.datetime ->
-            Helper.LibCall(com, "DateOffset", "fromDate", t, args, i.SignatureArgTypes, ?loc = r)
-            |> Some
         | _ ->
             let last = List.last args
 
@@ -2870,25 +2860,74 @@ let dates (com: ICompiler) (ctx: Context) r t (i: CallInfo) (thisArg: Expr optio
                 let argTypes = (List.take 6 i.SignatureArgTypes) @ [ Int32.Number; last.Type ]
 
                 Helper.LibCall(com, "Date", "create", t, args, argTypes, ?loc = r) |> Some
+
+            // JavaScript Date doesn't support microseconds precision
+            | 8, Number(Int32, NumberInfo.Empty) ->
+                "JavaScript Date with doesn't support microseconds precision"
+                |> addError com ctx.InlinePath r
+
+                None
+            // | 8, Number(_, NumberInfo.IsEnum ent) when ent.FullName = "System.DateTimeKind" ->
+            //     "JavaScript Date with doesn't support microseconds precision" |> addError com ctx.InlinePath r
+            //     None
+
             | _ ->
                 Helper.LibCall(com, moduleName, "create", t, args, i.SignatureArgTypes, ?loc = r)
                 |> Some
     | "ToString" ->
         Helper.LibCall(com, "Date", "toString", t, args, i.SignatureArgTypes, ?thisArg = thisArg, ?loc = r)
         |> Some
-    | "get_Kind"
-    | "get_Offset" as meth ->
-        let moduleName =
-            if meth = "get_Kind" then
-                "Date"
-            else
-                "DateOffset"
+    // | "get_Kind" ->
+    //     Helper.LibCall(com, moduleName, "kind", t, [ thisArg.Value ], [ thisArg.Value.Type ], ?loc = r)
+    //     |> Some
+    //     let y = DateTime.Now.UtcTicks
+    //     let x = DateTimeOffset.Now.UtcTicks
+    //     failwith "Not implemented"
 
+    | "get_Ticks" ->
+        Helper.LibCall(com, "Date", "getTicks", t, [ thisArg.Value ], [ thisArg.Value.Type ], ?loc = r)
+        |> Some
+    | meth ->
+        let args = ignoreFormatProvider meth args
         let meth = Naming.removeGetSetPrefix meth |> Naming.lowerFirst
 
-        Helper.LibCall(com, moduleName, meth, t, [ thisArg.Value ], [ thisArg.Value.Type ], ?loc = r)
+        Helper.LibCall(com, moduleName, meth, t, args, i.SignatureArgTypes, ?thisArg = thisArg, ?loc = r)
+        |> Some
+
+
+let dateTimeOffset (com: ICompiler) (ctx: Context) r t (i: CallInfo) (thisArg: Expr option) (args: Expr list) =
+    let moduleName = "DateOffset"
+
+    match i.CompiledName with
+    | ".ctor" ->
+        match args with
+        | [] -> Helper.LibCall(com, moduleName, "minValue", t, [], [], ?loc = r) |> Some
+        | ExprType(Number(Int64, _)) :: _ ->
+            Helper.LibCall(com, moduleName, "fromTicks", t, args, i.SignatureArgTypes, ?loc = r)
+            |> Some
+        | ExprType(DeclaredType(e, [])) :: _ when e.FullName = Types.datetime ->
+            Helper.LibCall(com, moduleName, "fromDate", t, args, i.SignatureArgTypes, ?loc = r)
+            |> Some
+        | _ ->
+            let last = List.last args
+
+            match args.Length, last.Type with
+            | 7, Number(_, NumberInfo.IsEnum ent) when ent.FullName = "System.DateTimeKind" ->
+                let args = (List.take 6 args) @ [ makeIntConst 0; last ]
+
+                let argTypes = (List.take 6 i.SignatureArgTypes) @ [ Int32.Number; last.Type ]
+
+                Helper.LibCall(com, "Date", "create", t, args, argTypes, ?loc = r) |> Some
+
+            | _ ->
+                Helper.LibCall(com, moduleName, "create", t, args, i.SignatureArgTypes, ?loc = r)
+                |> Some
+    | "ToString" ->
+        Helper.LibCall(com, "Date", "toString", t, args, i.SignatureArgTypes, ?thisArg = thisArg, ?loc = r)
+        |> Some
+    | "get_Offset" ->
+        Helper.LibCall(com, moduleName, "offset", t, [ thisArg.Value ], [ thisArg.Value.Type ], ?loc = r)
         |> Some
-    // DateTimeOffset
     | "get_LocalDateTime" ->
         Helper.LibCall(com, "DateOffset", "toLocalTime", t, [ thisArg.Value ], [ thisArg.Value.Type ], ?loc = r)
         |> Some
@@ -2896,7 +2935,7 @@ let dates (com: ICompiler) (ctx: Context) r t (i: CallInfo) (thisArg: Expr optio
         Helper.LibCall(com, "DateOffset", "toUniversalTime", t, [ thisArg.Value ], [ thisArg.Value.Type ], ?loc = r)
         |> Some
     | "get_DateTime" ->
-        let kind = System.DateTimeKind.Unspecified |> int |> makeIntConst
+        let kind = DateTimeKind.Unspecified |> int |> makeIntConst
 
         Helper.LibCall(
             com,
@@ -2921,6 +2960,7 @@ let dates (com: ICompiler) (ctx: Context) r t (i: CallInfo) (thisArg: Expr optio
         Helper.LibCall(com, moduleName, meth, t, args, i.SignatureArgTypes, ?thisArg = thisArg, ?loc = r)
         |> Some
 
+
 let dateOnly (com: ICompiler) (ctx: Context) r t (i: CallInfo) (thisArg: Expr option) (args: Expr list) =
     match i.CompiledName with
     | ".ctor" when args.Length = 4 ->
@@ -3878,8 +3918,8 @@ let private replacedModules =
             "System.Console", console
             "System.Diagnostics.Debug", debug
             "System.Diagnostics.Debugger", debug
-            Types.datetime, dates
-            Types.datetimeOffset, dates
+            Types.datetime, dateTime
+            Types.datetimeOffset, dateTimeOffset
             Types.dateOnly, dateOnly
             Types.timeOnly, timeOnly
             Types.timespan, timeSpans
@@ -4054,11 +4094,11 @@ let tryType typ =
     | Builtin kind ->
         match kind with
         | BclGuid -> Some(Types.guid, guids, [])
-        | BclDateTime -> Some(Types.datetime, dates, [])
-        | BclDateTimeOffset -> Some(Types.datetimeOffset, dates, [])
+        | BclDateTime -> Some(Types.datetime, dateTime, [])
+        | BclDateTimeOffset -> Some(Types.datetimeOffset, dateTimeOffset, [])
         | BclDateOnly -> Some(Types.dateOnly, dateOnly, [])
         | BclTimeOnly -> Some(Types.timeOnly, timeOnly, [])
-        | BclTimer -> Some("System.Timers.Timer", timers, [])
+        | BclTimer -> Some(Types.timer, timers, [])
         | BclTimeSpan -> Some(Types.timespan, timeSpans, [])
         | BclHashSet genArg -> Some(Types.hashset, hashSets, [ genArg ])
         | BclDictionary(key, value) -> Some(Types.dictionary, dictionaries, [ key; value ])
diff --git a/src/Fable.Transforms/Transforms.Util.fs b/src/Fable.Transforms/Transforms.Util.fs
index cd6e606063..0da5b2be76 100644
--- a/src/Fable.Transforms/Transforms.Util.fs
+++ b/src/Fable.Transforms/Transforms.Util.fs
@@ -204,6 +204,9 @@ module Types =
     [<Literal>]
     let timeOnly = "System.TimeOnly"
 
+    [<Literal>]
+    let timer = "System.Timers.Timer"
+
     [<Literal>]
     let int8 = "System.SByte"
 
diff --git a/src/fable-library-ts/Date.ts b/src/fable-library-ts/Date.ts
index d06fdbf7ce..02e5da1216 100644
--- a/src/fable-library-ts/Date.ts
+++ b/src/fable-library-ts/Date.ts
@@ -15,6 +15,360 @@ import { compareDates, DateKind, dateOffset, IDateTime, IDateTimeOffset, padWith
 export type OffsetInMinutes = number;
 export type Offset = "Z" | OffsetInMinutes | null;
 
+const shortDays =
+  [
+    "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
+  ]
+
+const longDays =
+  [
+    "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
+  ]
+
+const shortMonths =
+  [
+    "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
+  ]
+
+const longMonths =
+  [
+    "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"
+  ]
+
+
+function parseRepeatToken(format: string, pos: number, patternChar: string) {
+  let tokenLength = 0;
+  let internalPos = pos;
+  while (internalPos < format.length && format[internalPos] === patternChar) {
+    internalPos++;
+    tokenLength++;
+  }
+
+  return tokenLength;
+}
+
+function parseNextChar(format: string, pos: number) {
+  if (pos >= format.length - 1) {
+    return -1
+  }
+
+  return format.charCodeAt(pos + 1);
+}
+
+function parseQuotedString(format: string, pos: number) : [string, number] {
+  let beginPos = pos;
+  // Get the character used to quote the string
+  const quoteChar = format[pos];
+
+  let result = "";
+  let foundQuote = false;
+
+  while (pos < format.length) {
+    pos++;
+    const currentChar = format[pos];
+    if (currentChar === quoteChar) {
+      foundQuote = true;
+      break;
+    } else if (currentChar === "\\") {
+      if (pos < format.length) {
+        pos++;
+        result += format[pos];
+      } else {
+        // This means that '\' is the last character in the string.
+        throw new Error("Invalid string format");
+      }
+    } else {
+      result += currentChar;
+    }
+  }
+
+  if (!foundQuote) {
+    // We could not find the matching quote
+    throw new Error(`Invalid string format could not find matching quote for ${quoteChar}`);
+  }
+
+  return [result, pos - beginPos + 1];
+}
+
+function dateToStringWithCustomFormat(date: Date, format: string, utc: boolean) {
+  let cursorPos = 0;
+  let tokenLength = 0;
+  let result = "";
+  const localizedDate = utc ? DateTime(date.getTime(), DateKind.UTC) : date;
+
+  while (cursorPos < format.length) {
+    const token = format[cursorPos];
+
+    switch (token) {
+      case "d":
+        tokenLength = parseRepeatToken(format, cursorPos, "d");
+        cursorPos += tokenLength;
+        switch (tokenLength) {
+          case 1:
+            result += localizedDate.getDate();
+            break;
+          case 2:
+            result += padWithZeros(localizedDate.getDate(), 2);
+            break;
+          case 3:
+            result += shortDays[dayOfWeek(localizedDate)];
+            break;
+          case 4:
+            result += longDays[dayOfWeek(localizedDate)];
+            break;
+          default:
+            break;
+        }
+        break;
+      case "f":
+        tokenLength = parseRepeatToken(format, cursorPos, "f");
+        cursorPos += tokenLength;
+        if (tokenLength <= 3) {
+          const precision = 10 ** (3 - tokenLength);
+          result += padWithZeros(Math.floor(millisecond(localizedDate) / precision), tokenLength);
+        } else if (tokenLength <= 7) {
+          // JavaScript Date only support precision to the millisecond
+          // so we fill the rest of the precision with 0 as if the date didn't have
+          // milliseconds provided to it.
+          // This is to have the same behavior as .NET when doing:
+          // DateTime(1, 2, 3, 4, 5, 6, DateTimeKind.Utc).ToString("fffff") => 00000
+          result += (""+millisecond(localizedDate)).padEnd(tokenLength, "0");
+        }
+        break;
+      case "F":
+        tokenLength = parseRepeatToken(format, cursorPos, "F");
+        cursorPos += tokenLength;
+        if (tokenLength <= 3) {
+          const precision = 10 ** (3 - tokenLength);
+          const value = Math.floor(millisecond(localizedDate) / precision)
+          if (value != 0) {
+            result += padWithZeros(value, tokenLength);
+          }
+        } else if (tokenLength <= 7) {
+          // JavaScript Date only support precision to the millisecond
+          // so we can't go beyond that.
+          // We also need to pad start with 0 if the value is not 0
+          const value = millisecond(localizedDate);
+          if (value != 0) {
+            result += padWithZeros(value, 3);
+          }
+        }
+        break;
+      case "g":
+        tokenLength = parseRepeatToken(format, cursorPos, "g");
+        cursorPos += tokenLength;
+        if (tokenLength <= 2) {
+          result += "A.D.";
+        }
+        break;
+      case "h":
+        tokenLength = parseRepeatToken(format, cursorPos, "h");
+        cursorPos += tokenLength;
+        switch (tokenLength) {
+          case 1:
+            result += hour(localizedDate) % 12
+            break;
+          case 2:
+            result += padWithZeros(hour(localizedDate) % 12, 2);
+            break;
+          default:
+            break;
+        }
+        break;
+      case "H":
+        tokenLength = parseRepeatToken(format, cursorPos, "H");
+        cursorPos += tokenLength;
+        switch (tokenLength) {
+          case 1:
+            result += hour(localizedDate);
+            break;
+          case 2:
+            result += padWithZeros(hour(localizedDate), 2);
+            break;
+          default:
+            break;
+        }
+        break;
+      case "K":
+        tokenLength = parseRepeatToken(format, cursorPos, "K");
+        cursorPos += tokenLength;
+        switch (tokenLength) {
+          case 1:
+            switch (kind(localizedDate)) {
+              case DateKind.UTC:
+                result += "Z";
+                break;
+              case DateKind.Local:
+                result += dateOffsetToString(localizedDate.getTimezoneOffset() * -60000);
+                break;
+              case DateKind.Unspecified:
+                break;
+            }
+            break;
+          default:
+            break;
+        }
+        break;
+      case "m":
+        tokenLength = parseRepeatToken(format, cursorPos, "m");
+        cursorPos += tokenLength;
+        switch (tokenLength) {
+          case 1:
+            result += minute(localizedDate);
+            break;
+          case 2:
+            result += padWithZeros(minute(localizedDate), 2);
+            break;
+          default:
+            break;
+        }
+        break;
+      case "M":
+        tokenLength = parseRepeatToken(format, cursorPos, "M");
+        cursorPos += tokenLength;
+        switch (tokenLength) {
+          case 1:
+            result += month(localizedDate);
+            break;
+          case 2:
+            result += padWithZeros(month(localizedDate), 2);
+            break;
+          case 3:
+            result += shortMonths[month(localizedDate) - 1];
+            break;
+          case 4:
+            result += longMonths[month(localizedDate) - 1];
+            break;
+          default:
+            break;
+        }
+        break;
+      case "s":
+        tokenLength = parseRepeatToken(format, cursorPos, "s");
+        cursorPos += tokenLength;
+        switch (tokenLength) {
+          case 1:
+            result += second(localizedDate);
+            break;
+          case 2:
+            result += padWithZeros(second(localizedDate), 2);
+            break;
+          default:
+            break;
+        }
+        break;
+      case "t":
+        tokenLength = parseRepeatToken(format, cursorPos, "t");
+        cursorPos += tokenLength;
+        switch (tokenLength) {
+          case 1:
+            result += localizedDate.getHours() < 12 ? "A" : "P";
+            break;
+          case 2:
+            result += localizedDate.getHours() < 12 ? "AM" : "PM";
+            break;
+          default:
+            break;
+        }
+        break;
+      case "y":
+        tokenLength = parseRepeatToken(format, cursorPos, "y");
+        cursorPos += tokenLength;
+        switch (tokenLength) {
+          case 1:
+            result += localizedDate.getFullYear() % 100;
+            break;
+          case 2:
+            result += padWithZeros(localizedDate.getFullYear() % 100, 2);
+            break;
+          case 3:
+            result += padWithZeros(localizedDate.getFullYear(), 3);
+            break;
+          case 4:
+            result += padWithZeros(localizedDate.getFullYear(), 4);
+            break;
+          case 5:
+            result += padWithZeros(localizedDate.getFullYear(), 5);
+            break;
+          default:
+            break;
+        }
+        break;
+      case "z":
+        tokenLength = parseRepeatToken(format, cursorPos, "z");
+        cursorPos += tokenLength;
+        let utcOffsetText = "";
+
+        switch (kind(localizedDate)) {
+          case DateKind.UTC:
+            utcOffsetText = "+00:00";
+            break;
+          case DateKind.Local:
+            utcOffsetText = dateOffsetToString(localizedDate.getTimezoneOffset() * -60000);
+            break;
+          case DateKind.Unspecified:
+            utcOffsetText = dateOffsetToString(toLocalTime(localizedDate).getTimezoneOffset() * -60000);
+            break;
+        }
+
+        const sign = utcOffsetText[0] === "-" ? "-" : "+";
+        const hours = parseInt(utcOffsetText.substring(1, 3), 10);
+        const minutes = parseInt(utcOffsetText.substring(4, 6), 10);
+
+        switch (tokenLength) {
+          case 1:
+            result += `${sign}${hours}`;
+            break;
+          case 2:
+            result += `${sign}${padWithZeros(hours, 2)}`;
+            break;
+          default:
+            result += `${sign}${padWithZeros(hours, 2)}:${padWithZeros(minutes, 2)}`;
+            break;
+        }
+        break;
+      case ":":
+        result += ":";
+        cursorPos++;
+        break;
+      case "/":
+        result += "/";
+        cursorPos++;
+        break;
+      case "'":
+      case '"':
+        const [quotedString, quotedStringLenght] = parseQuotedString(format, cursorPos);
+        result += quotedString;
+        cursorPos += quotedStringLenght;
+        break;
+      case "%":
+        const nextChar = parseNextChar(format, cursorPos);
+        if (nextChar >= 0 && nextChar !== "%".charCodeAt(0)) {
+          cursorPos += 2;
+          result += dateToStringWithCustomFormat(localizedDate, String.fromCharCode(nextChar), utc);
+        } else {
+          throw new Error("Invalid format string");
+        }
+        break;
+      case "\\":
+        const nextChar2 = parseNextChar(format, cursorPos);
+        if (nextChar2 >= 0) {
+          cursorPos += 2;
+          result += String.fromCharCode(nextChar2);
+        } else {
+          throw new Error("Invalid format string");
+        }
+        break;
+      default:
+        cursorPos++;
+        result += token;
+        break;
+    }
+  }
+
+  return result;
+}
+
 export function kind(value: IDateTime): number {
   return value.kind || 0;
 }
@@ -66,31 +420,6 @@ function dateToISOStringWithOffset(dateWithOffset: Date, offset: number) {
   return str.substring(0, str.length - 1) + dateOffsetToString(offset);
 }
 
-function dateToStringWithCustomFormat(date: Date, format: string, utc: boolean) {
-  return format.replace(/(\w)\1*/g, (match: string) => {
-    let rep = Number.NaN;
-    switch (match.substring(0, 1)) {
-      case "y":
-        const y = utc ? date.getUTCFullYear() : date.getFullYear();
-        rep = match.length < 4 ? y % 100 : y; break;
-      case "M": rep = (utc ? date.getUTCMonth() : date.getMonth()) + 1; break;
-      case "d": rep = utc ? date.getUTCDate() : date.getDate(); break;
-      case "H": rep = utc ? date.getUTCHours() : date.getHours(); break;
-      case "h":
-        const h = utc ? date.getUTCHours() : date.getHours();
-        rep = h > 12 ? h % 12 : h; break;
-      case "m": rep = utc ? date.getUTCMinutes() : date.getMinutes(); break;
-      case "s": rep = utc ? date.getUTCSeconds() : date.getSeconds(); break;
-      case "f": rep = utc ? date.getUTCMilliseconds() : date.getMilliseconds(); break;
-    }
-    if (Number.isNaN(rep)) {
-      return match;
-    } else {
-      return padWithZeros(rep, match.length);
-    }
-  });
-}
-
 function dateToStringWithOffset(date: IDateTimeOffset, format?: string) {
   const d = new Date(date.getTime() + (date.offset ?? 0));
   if (typeof format !== "string") {
diff --git a/src/fable-library-ts/Util.ts b/src/fable-library-ts/Util.ts
index 04bcbda519..9bcb089558 100644
--- a/src/fable-library-ts/Util.ts
+++ b/src/fable-library-ts/Util.ts
@@ -270,22 +270,11 @@ export function lazyFromValue<T>(v: T) {
 }
 
 export function padWithZeros(i: number, length: number) {
-  let str = i.toString(10);
-  while (str.length < length) {
-    str = "0" + str;
-  }
-  return str;
+  return i.toString(10).padStart(length, "0");
 }
 
 export function padLeftAndRightWithZeros(i: number, lengthLeft: number, lengthRight: number) {
-  let str = i.toString(10);
-  while (str.length < lengthLeft) {
-    str = "0" + str;
-  }
-  while (str.length < lengthRight) {
-    str = str + "0";
-  }
-  return str;
+  return i.toString(10).padStart(lengthLeft, "0").padEnd(lengthRight, "0");
 }
 
 export function dateOffset(date: IDateTime | IDateTimeOffset): number {
diff --git a/src/quicktest/tsconfig.json b/src/quicktest/tsconfig.json
index d913ed8487..26fdd2d8a5 100644
--- a/src/quicktest/tsconfig.json
+++ b/src/quicktest/tsconfig.json
@@ -12,6 +12,7 @@
     "noEmitOnError": true,
     "newLine": "lf",
     "forceConsistentCasingInFileNames": true,
-    "preserveWatchOutput": true
+    "preserveWatchOutput": true,
+    "moduleResolution": "Node"
   }
 }
diff --git a/tests/Js/Main/DateTimeTests.fs b/tests/Js/Main/DateTimeTests.fs
index b2d2a22907..e9c2727d79 100644
--- a/tests/Js/Main/DateTimeTests.fs
+++ b/tests/Js/Main/DateTimeTests.fs
@@ -21,8 +21,354 @@ let thatYearMilliseconds (dt: DateTime) =
 let tests =
   testList "DateTime" [
     testCase "DateTime.ToString with custom format works" <| fun () ->
-        DateTime(2014, 9, 11, 16, 37, 0).ToString("HH:mm", CultureInfo.InvariantCulture)
-        |> equal "16:37"
+        DateTime(2014, 7, 1, 16, 37, 1, 2).ToString("r d", CultureInfo.InvariantCulture)
+        |> equal "r 1"
+        DateTime(2014, 7, 13, 16, 37, 1, 2).ToString("r d", CultureInfo.InvariantCulture)
+        |> equal "r 13"
+
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r dd", CultureInfo.InvariantCulture)
+        |> equal "r 01"
+        DateTime(2014, 7, 21, 16, 37, 0).ToString("r dd", CultureInfo.InvariantCulture)
+        |> equal "r 21"
+
+        DateTime(2014, 7, 7, 16, 37, 0).ToString("r ddd", CultureInfo.InvariantCulture)
+        |> equal "r Mon"
+        DateTime(2014, 7, 8, 16, 37, 0).ToString("r ddd", CultureInfo.InvariantCulture)
+        |> equal "r Tue"
+        DateTime(2014, 7, 9, 16, 37, 0).ToString("r ddd", CultureInfo.InvariantCulture)
+        |> equal "r Wed"
+        DateTime(2014, 7, 10, 16, 37, 0).ToString("r ddd", CultureInfo.InvariantCulture)
+        |> equal "r Thu"
+        DateTime(2014, 7, 11, 16, 37, 0).ToString("r ddd", CultureInfo.InvariantCulture)
+        |> equal "r Fri"
+        DateTime(2014, 7, 12, 16, 37, 0).ToString("r ddd", CultureInfo.InvariantCulture)
+        |> equal "r Sat"
+        DateTime(2014, 7, 13, 16, 37, 0).ToString("r ddd", CultureInfo.InvariantCulture)
+        |> equal "r Sun"
+
+        DateTime(2014, 7, 7, 16, 37, 0).ToString("r dddd", CultureInfo.InvariantCulture)
+        |> equal "r Monday"
+        DateTime(2014, 7, 8, 16, 37, 0).ToString("r dddd", CultureInfo.InvariantCulture)
+        |> equal "r Tuesday"
+        DateTime(2014, 7, 9, 16, 37, 0).ToString("r dddd", CultureInfo.InvariantCulture)
+        |> equal "r Wednesday"
+        DateTime(2014, 7, 10, 16, 37, 0).ToString("r dddd", CultureInfo.InvariantCulture)
+        |> equal "r Thursday"
+        DateTime(2014, 7, 11, 16, 37, 0).ToString("r dddd", CultureInfo.InvariantCulture)
+        |> equal "r Friday"
+        DateTime(2014, 7, 12, 16, 37, 0).ToString("r dddd", CultureInfo.InvariantCulture)
+        |> equal "r Saturday"
+        DateTime(2014, 7, 13, 16, 37, 0).ToString("r dddd", CultureInfo.InvariantCulture)
+        |> equal "r Sunday"
+
+        DateTime.Parse("2009-06-15T13:45:30.6175425").ToString("r f", CultureInfo.InvariantCulture)
+        |> equal "r 6"
+        DateTime.Parse("2009-06-15T13:45:30.05").ToString("r f", CultureInfo.InvariantCulture)
+        |> equal "r 0"
+        DateTime.Parse("2009-06-15T13:45:30.6175425").ToString("r ff", CultureInfo.InvariantCulture)
+        |> equal "r 61"
+        DateTime.Parse("2009-06-15T13:45:30.0050000").ToString("r ff", CultureInfo.InvariantCulture)
+        |> equal "r 00"
+        DateTime.Parse("2009-06-15T13:45:30.6175425").ToString("r fff", CultureInfo.InvariantCulture)
+        |> equal "r 617"
+        DateTime.Parse("2009-06-15T13:45:30.0005000").ToString("r fff", CultureInfo.InvariantCulture)
+        |> equal "r 000"
+        // JavaScript Date only support precision to the millisecond so we fill with 0
+        DateTime.Parse("2009-06-15T13:45:30.617").ToString("r ffff", CultureInfo.InvariantCulture)
+        |> equal "r 6170"
+        DateTime.Parse("2009-06-15T13:45:30.000").ToString("r ffff", CultureInfo.InvariantCulture)
+        |> equal "r 0000"
+        DateTime.Parse("2009-06-15T13:45:30.617").ToString("r fffff", CultureInfo.InvariantCulture)
+        |> equal "r 61700"
+        DateTime.Parse("2009-06-15T13:45:30.000").ToString("r fffff", CultureInfo.InvariantCulture)
+        |> equal "r 00000"
+        DateTime.Parse("2009-06-15T13:45:30.617").ToString("r ffffff", CultureInfo.InvariantCulture)
+        |> equal "r 617000"
+        DateTime.Parse("2009-06-15T13:45:30.000").ToString("r ffffff", CultureInfo.InvariantCulture)
+        |> equal "r 000000"
+        DateTime.Parse("2009-06-15T13:45:30.617").ToString("r fffffff", CultureInfo.InvariantCulture)
+        |> equal "r 6170000"
+
+        DateTime.Parse("2009-06-15T13:45:30.6175425").ToString("r F", CultureInfo.InvariantCulture)
+        |> equal "r 6"
+        DateTime.Parse("2009-06-15T13:45:30.05").ToString("r F", CultureInfo.InvariantCulture)
+        |> equal "r "
+        DateTime.Parse("2009-06-15T13:45:30.6175425").ToString("r FF", CultureInfo.InvariantCulture)
+        |> equal "r 61"
+        DateTime.Parse("2009-06-15T13:45:30.0050000").ToString("r FF", CultureInfo.InvariantCulture)
+        |> equal "r "
+        DateTime.Parse("2009-06-15T13:45:30.6175425").ToString("r FFF", CultureInfo.InvariantCulture)
+        |> equal "r 617"
+        DateTime.Parse("2009-06-15T13:45:30.0005000").ToString("r FFF", CultureInfo.InvariantCulture)
+        |> equal "r "
+        // JavaScript Date only support precision to the millisecond so we fill with 0
+        DateTime.Parse("2009-06-15T13:45:30.617").ToString("r FFFF", CultureInfo.InvariantCulture)
+        |> equal "r 617"
+        DateTime.Parse("2009-06-15T13:45:30.000").ToString("r FFFF", CultureInfo.InvariantCulture)
+        |> equal "r "
+        DateTime.Parse("2009-06-15T13:45:30.617").ToString("r FFFFF", CultureInfo.InvariantCulture)
+        |> equal "r 617"
+        DateTime.Parse("2009-06-15T13:45:30.000").ToString("r FFFFF", CultureInfo.InvariantCulture)
+        |> equal "r "
+        DateTime.Parse("2009-06-15T13:45:30.061").ToString("r FFFFFF", CultureInfo.InvariantCulture)
+        |> equal "r 061"
+        DateTime.Parse("2009-06-15T13:45:30.000").ToString("r FFFFFF", CultureInfo.InvariantCulture)
+        |> equal "r "
+        DateTime.Parse("2009-06-15T13:45:30.617").ToString("r FFFFFFF", CultureInfo.InvariantCulture)
+        |> equal "r 617"
+        DateTime.Parse("2009-06-15T13:45:30.000").ToString("r FFFFFFF", CultureInfo.InvariantCulture)
+        |> equal "r "
+
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r g", CultureInfo.InvariantCulture)
+        |> equal "r A.D."
+
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r gg", CultureInfo.InvariantCulture)
+        |> equal "r A.D."
+
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r h", CultureInfo.InvariantCulture)
+        |> equal "r 4"
+        DateTime(2014, 7, 1, 4, 37, 0).ToString("r h", CultureInfo.InvariantCulture)
+        |> equal "r 4"
+
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r hh", CultureInfo.InvariantCulture)
+        |> equal "r 04"
+        DateTime(2014, 7, 1, 4, 37, 0).ToString("r hh", CultureInfo.InvariantCulture)
+        |> equal "r 04"
+
+        DateTime(2014, 7, 1, 4, 37, 0).ToString("r H", CultureInfo.InvariantCulture)
+        |> equal "r 4"
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r H", CultureInfo.InvariantCulture)
+        |> equal "r 16"
+
+        DateTime(2014, 7, 1, 4, 37, 0).ToString("r HH", CultureInfo.InvariantCulture)
+        |> equal "r 04"
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r HH", CultureInfo.InvariantCulture)
+        |> equal "r 16"
+
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r K", CultureInfo.InvariantCulture)
+        |> equal "r "
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Utc).ToString("r K", CultureInfo.InvariantCulture)
+        |> equal "r Z"
+
+        // // Timezone dependent (test is configured for Europe/Paris timezone)
+        // DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Local).ToString("r K", CultureInfo.InvariantCulture)
+        // |> equal "r +02:00"
+
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Unspecified).ToString("r K", CultureInfo.InvariantCulture)
+        |> equal "r "
+
+        DateTime(2014, 7, 1, 16, 3, 0).ToString("r m", CultureInfo.InvariantCulture)
+        |> equal "r 3"
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r m", CultureInfo.InvariantCulture)
+        |> equal "r 37"
+
+        DateTime(2014, 7, 1, 16, 3, 0).ToString("r mm", CultureInfo.InvariantCulture)
+        |> equal "r 03"
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r mm", CultureInfo.InvariantCulture)
+        |> equal "r 37"
+
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r M", CultureInfo.InvariantCulture)
+        |> equal "r 7"
+        DateTime(2014, 11, 1, 16, 37, 0).ToString("r M", CultureInfo.InvariantCulture)
+        |> equal "r 11"
+
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r MM", CultureInfo.InvariantCulture)
+        |> equal "r 07"
+        DateTime(2014, 11, 1, 16, 37, 0).ToString("r MM", CultureInfo.InvariantCulture)
+        |> equal "r 11"
+
+        DateTime(2014, 1, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r Jan"
+        DateTime(2014, 2, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r Feb"
+        DateTime(2014, 3, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r Mar"
+        DateTime(2014, 4, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r Apr"
+        DateTime(2014, 5, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r May"
+        DateTime(2014, 6, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r Jun"
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r Jul"
+        DateTime(2014, 8, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r Aug"
+        DateTime(2014, 9, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r Sep"
+        DateTime(2014, 10, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r Oct"
+        DateTime(2014, 11, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r Nov"
+        DateTime(2014, 12, 1, 16, 37, 0).ToString("r MMM", CultureInfo.InvariantCulture)
+        |> equal "r Dec"
+
+        DateTime(2014, 1, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r January"
+        DateTime(2014, 2, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r February"
+        DateTime(2014, 3, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r March"
+        DateTime(2014, 4, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r April"
+        DateTime(2014, 5, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r May"
+        DateTime(2014, 6, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r June"
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r July"
+        DateTime(2014, 8, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r August"
+        DateTime(2014, 9, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r September"
+        DateTime(2014, 10, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r October"
+        DateTime(2014, 11, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r November"
+        DateTime(2014, 12, 1, 16, 37, 0).ToString("r MMMM", CultureInfo.InvariantCulture)
+        |> equal "r December"
+
+        DateTime(2014, 7, 1, 16, 37, 3).ToString("r s", CultureInfo.InvariantCulture)
+        |> equal "r 3"
+        DateTime(2014, 7, 1, 16, 37, 31).ToString("r s", CultureInfo.InvariantCulture)
+        |> equal "r 31"
+
+        DateTime(2014, 7, 1, 16, 37, 3).ToString("r ss", CultureInfo.InvariantCulture)
+        |> equal "r 03"
+        DateTime(2014, 7, 1, 16, 37, 31).ToString("r ss", CultureInfo.InvariantCulture)
+        |> equal "r 31"
+
+        DateTime(2014, 7, 1, 1, 37, 0).ToString("r t", CultureInfo.InvariantCulture)
+        |> equal "r A"
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r t", CultureInfo.InvariantCulture)
+        |> equal "r P"
+        DateTime(2014, 7, 1, 1, 37, 0).ToString("r tt", CultureInfo.InvariantCulture)
+        |> equal "r AM"
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r tt", CultureInfo.InvariantCulture)
+        |> equal "r PM"
+
+        DateTime(1,1,1).ToString("r y", CultureInfo.InvariantCulture)
+        |> equal "r 1"
+        DateTime(0900,1,1).ToString("r y", CultureInfo.InvariantCulture)
+        |> equal "r 0"
+        DateTime(1900,1,1).ToString("r y", CultureInfo.InvariantCulture)
+        |> equal "r 0"
+        DateTime(2009,1,1).ToString("r y", CultureInfo.InvariantCulture)
+        |> equal "r 9"
+        DateTime(2019,1,1).ToString("r y", CultureInfo.InvariantCulture)
+        |> equal "r 19"
+
+        DateTime(1,1,1).ToString("r yy", CultureInfo.InvariantCulture)
+        |> equal "r 01"
+        DateTime(0900,1,1).ToString("r yy", CultureInfo.InvariantCulture)
+        |> equal "r 00"
+        DateTime(1900,1,1).ToString("r yy", CultureInfo.InvariantCulture)
+        |> equal "r 00"
+        DateTime(2009,1,1).ToString("r yy", CultureInfo.InvariantCulture)
+        |> equal "r 09"
+        DateTime(2019,1,1).ToString("r yy", CultureInfo.InvariantCulture)
+        |> equal "r 19"
+
+        DateTime(1,1,1).ToString("r yyy", CultureInfo.InvariantCulture)
+        |> equal "r 001"
+        DateTime(0900,1,1).ToString("r yyy", CultureInfo.InvariantCulture)
+        |> equal "r 900"
+        DateTime(1900,1,1).ToString("r yyy", CultureInfo.InvariantCulture)
+        |> equal "r 1900"
+        DateTime(2009,1,1).ToString("r yyy", CultureInfo.InvariantCulture)
+        |> equal "r 2009"
+        DateTime(2019,1,1).ToString("r yyy", CultureInfo.InvariantCulture)
+        |> equal "r 2019"
+
+        DateTime(1,1,1).ToString("r yyyy", CultureInfo.InvariantCulture)
+        |> equal "r 0001"
+        DateTime(0900,1,1).ToString("r yyyy", CultureInfo.InvariantCulture)
+        |> equal "r 0900"
+        DateTime(1900,1,1).ToString("r yyyy", CultureInfo.InvariantCulture)
+        |> equal "r 1900"
+        DateTime(2009,1,1).ToString("r yyyy", CultureInfo.InvariantCulture)
+        |> equal "r 2009"
+        DateTime(2019,1,1).ToString("r yyyy", CultureInfo.InvariantCulture)
+        |> equal "r 2019"
+
+
+        DateTime(1,1,1).ToString("r yyyyy", CultureInfo.InvariantCulture)
+        |> equal "r 00001"
+        DateTime(0900,1,1).ToString("r yyyyy", CultureInfo.InvariantCulture)
+        |> equal "r 00900"
+        DateTime(1900,1,1).ToString("r yyyyy", CultureInfo.InvariantCulture)
+        |> equal "r 01900"
+        DateTime(2009,1,1).ToString("r yyyyy", CultureInfo.InvariantCulture)
+        |> equal "r 02009"
+        DateTime(2019,1,1).ToString("r yyyyy", CultureInfo.InvariantCulture)
+        |> equal "r 02019"
+
+
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Utc).ToString("r z", CultureInfo.InvariantCulture)
+        |> equal "r +0"
+
+        // Timezone dependent (test is configured for Europe/Paris timezone)
+        // DateTime(2014, 7, 1, 16, 37, 0).ToString("r z", CultureInfo.InvariantCulture)
+        // |> equal "r +2"
+        // DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Local).ToString("r z", CultureInfo.InvariantCulture)
+        // |> equal "r +2"
+
+
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Utc).ToString("r zz", CultureInfo.InvariantCulture)
+        |> equal "r +00"
+        // Timezone dependent (test is configured for Europe/Paris timezone)
+        // DateTime(2014, 7, 1, 16, 37, 0).ToString("r zz", CultureInfo.InvariantCulture)
+        // |> equal "r +02"
+        // DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Local).ToString("r zz", CultureInfo.InvariantCulture)
+        // |> equal "r +02"
+
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Utc).ToString("r zzz", CultureInfo.InvariantCulture)
+        |> equal "r +00:00"
+        // Timezone dependent (test is configured for Europe/Paris timezone)
+        // DateTime(2014, 7, 1, 16, 37, 0).ToString("r zzz", CultureInfo.InvariantCulture)
+        // |> equal "r +02:00"
+        // DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Local).ToString("r zzz", CultureInfo.InvariantCulture)
+        // |> equal "r +02:00"
+
+        // Time separator
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r :", CultureInfo.InvariantCulture)
+        |> equal "r :"
+
+        // Date separator
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r /", CultureInfo.InvariantCulture)
+        |> equal "r /"
+
+        // String quotation
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r \"hh\" h", CultureInfo.InvariantCulture)
+        |> equal "r hh 4"
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r 'hh' h", CultureInfo.InvariantCulture)
+        |> equal "r hh 4"
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r \'hh\'", CultureInfo.InvariantCulture)
+        |> equal "r hh"
+
+        // Format character
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r %h", CultureInfo.InvariantCulture)
+        |> equal "r 4"
+        DateTime(2014, 7, 1, 16, 37, 0).ToString("r %hh", CultureInfo.InvariantCulture)
+        |> equal "r 44"
+
+        // Escape character
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Utc).ToString("r \zz", CultureInfo.InvariantCulture)
+        |> equal "r z+0"
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Utc).ToString("r \\zz", CultureInfo.InvariantCulture)
+        |> equal "r z+0"
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Utc).ToString("r \\\zz", CultureInfo.InvariantCulture)
+        |> equal "r \+00"
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Utc).ToString("r \\z\\z", CultureInfo.InvariantCulture)
+        |> equal "r zz"
+
+        // Escape character with verbatim string
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Utc).ToString("""r \zz""", CultureInfo.InvariantCulture)
+        |> equal "r z+0"
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Utc).ToString("""r \\zz""", CultureInfo.InvariantCulture)
+        |> equal "r \+00"
+        DateTime(2014, 7, 1, 16, 37, 0, DateTimeKind.Utc).ToString("""r \\\zz""", CultureInfo.InvariantCulture)
+        |> equal "r \z+0"
+
 
     testCase "DateTime.ToString without separator works" <| fun () -> // See #1131
         DateTime(2017, 9, 5).ToString("yyyyMM")