diff --git a/README.md b/README.md
index 095913b..daa962d 100644
--- a/README.md
+++ b/README.md
@@ -2,4 +2,5 @@
 
 **WARNING**: This project is in its alpha phase and not yet production-ready. Use it with care!
 
-`js-ffi` is a library allowing you to interact with basic JavaScript constructs from MoonBit.
+`js-ffi` is a library allowing you to interact with basic JavaScript constructs from MoonBit, 
+ensuring as much null-safety as possible.
diff --git a/src/js/async.mbt b/src/js/async.mbt
index 54d9672..d8ac430 100644
--- a/src/js/async.mbt
+++ b/src/js/async.mbt
@@ -26,7 +26,7 @@ extern "js" fn Promise::wait_ffi(
 
 ///|
 pub async fn Promise::wait(self : Promise) -> Value! {
-  suspend!!(fn(k, ke) { Promise::wait_ffi(self, k, fn(e) { ke(Error_(e)) }) })
+  suspend!(fn(k, ke) { Promise::wait_ffi(self, k, fn(e) { ke(Error_(e)) }) })
 }
 
 ///|
@@ -39,7 +39,7 @@ pub async fn Promise::wait(self : Promise) -> Value! {
 ///
 /// If you don't care about the result of the operation, you can use `spawn_detach` instead.
 pub fn Promise::unsafe_new[T](op : async () -> T!) -> Promise {
-  Promise::new_ffi(fn() { Value::cast_from(op!!()) })
+  Promise::new_ffi(fn() { Value::from(op!()) })
 }
 
 ///|
@@ -50,7 +50,7 @@ extern "js" fn Promise::new_ffi(op : async () -> Value!) -> Promise =
 pub fn spawn_detach[T, E : Error](op : async () -> T!E) -> Unit {
   async_run(fn() {
     try {
-      op!!() |> ignore
+      op!() |> ignore
     } catch {
       _ => ()
     }
@@ -65,21 +65,21 @@ pub extern "js" fn Promise::all(promises : Array[Promise]) -> Promise = "(ps) =>
 ///|
 /// Wraps each given `async fn` in a `Promise` and waits for all of them to resolve.
 pub async fn async_all![T](ops : Array[async () -> T!]) -> Array[T] {
-  async_all_raw!!(ops.map(fn(op) { async fn!() { Value::cast_from(op!!()) } })).map(
-    Value::cast,
+  async_all_raw!(ops.map(fn(op) { async fn!() { Value::from(op!()) } })).map(
+    Value::unsafe_into,
   )
 }
 
 ///|
 async fn async_all_raw!(ops : Array[async () -> Value!]) -> Array[Value] {
-  Promise::all(ops.map(Promise::unsafe_new)).wait!!().cast()
+  Promise::all(ops.map(Promise::unsafe_new)).wait!().unsafe_into()
 }
 
 ///|
 pub fn async_test(op : async () -> Unit!) -> Unit {
   async_run(async fn() {
     try {
-      op!!()
+      op!()
     } catch {
       e => {
         println("ERROR in `async_test`: \{e}")
diff --git a/src/js/async_deprecated.mbt b/src/js/async_deprecated.mbt
index f3b6d66..09f939b 100644
--- a/src/js/async_deprecated.mbt
+++ b/src/js/async_deprecated.mbt
@@ -12,13 +12,13 @@ extern "js" fn async_wrap_ffi(
 ///|
 #deprecated("use Promise::wait instead")
 pub async fn async_wrap(op : AsyncOp) -> Value! {
-  suspend!!(fn(k, ke) { async_wrap_ffi(op, k, fn(e) { ke(Error_(e)) }) })
+  suspend!(fn(k, ke) { async_wrap_ffi(op, k, fn(e) { ke(Error_(e)) }) })
 }
 
 ///|
 #deprecated("use Promise::new instead")
 pub fn async_unwrap[T](op : async () -> T!) -> Promise {
-  Promise::new_ffi(fn() { Value::cast_from(op!!()) })
+  Promise::new_ffi(fn() { Value::from(op!()) })
 }
 
 ///|
diff --git a/src/js/async_test.mbt b/src/js/async_test.mbt
index f5979ed..6bcda65 100644
--- a/src/js/async_test.mbt
+++ b/src/js/async_test.mbt
@@ -5,7 +5,7 @@ async fn op1() -> String? {
 
 ///|
 async fn op2() -> String? {
-  guard op1!!() is Some(prefix)
+  guard op1!() is Some(prefix)
   Some(prefix + ", World")
 }
 
@@ -18,7 +18,7 @@ async fn op3() -> String? {
 test "Promise::wait" {
   @js.async_test(fn!() {
     // Promise::unsafe_new + Promise::wait is a noop.
-    let res = @js.Promise::unsafe_new(fn() { op1!!() }).wait!!()
+    let res = @js.Promise::unsafe_new(fn() { op1!() }).wait!()
     assert_eq!(res.cast(), Some("Hello"))
   })
 }
@@ -27,7 +27,7 @@ test "Promise::wait" {
 test "async_all" {
   @js.async_test(fn!() {
     assert_eq!(
-      @js.async_all!!([fn() { op2!!() }, fn() { op1!!() }, fn() { op3!!() }]),
+      @js.async_all!([fn() { op2!() }, fn() { op1!() }, fn() { op3!() }]),
       [Some("Hello, World"), Some("Hello"), None],
     )
   })
diff --git a/src/js/cast.mbt b/src/js/cast.mbt
index eebf440..925c897 100644
--- a/src/js/cast.mbt
+++ b/src/js/cast.mbt
@@ -46,7 +46,7 @@ pub impl Cast for String with into(value) {
 
 ///|
 pub impl Cast for String with from(value) {
-  Value::cast_from(value)
+  Value::from(value)
 }
 
 ///|
@@ -56,7 +56,7 @@ pub impl Cast for Int with into(value) {
 
 ///|
 pub impl Cast for Int with from(value) {
-  Value::cast_from(value)
+  Value::from(value)
 }
 
 ///|
@@ -66,7 +66,7 @@ pub impl Cast for Double with into(value) {
 
 ///|
 pub impl Cast for Double with from(value) {
-  Value::cast_from(value)
+  Value::from(value)
 }
 
 ///|
@@ -76,7 +76,7 @@ pub impl Cast for Bool with into(value) {
 
 ///|
 pub impl Cast for Bool with from(value) {
-  Value::cast_from(value)
+  Value::from(value)
 }
 
 ///|
@@ -86,7 +86,7 @@ pub impl[A : Cast] Cast for Array[A] with into(value) {
   .bind(fn(arr) {
     let is_type_a = fn(elem) { not((Cast::into(elem) : A?).is_empty()) }
     if arr.iter().all(is_type_a) {
-      Some(Value::cast_from(arr).cast())
+      Some(Value::from(arr).unsafe_into())
     } else {
       None
     }
@@ -95,5 +95,5 @@ pub impl[A : Cast] Cast for Array[A] with into(value) {
 
 ///|
 pub impl[A : Cast] Cast for Array[A] with from(value) {
-  Value::cast_from(value)
+  Value::from(value)
 }
diff --git a/src/js/error.mbt b/src/js/error.mbt
index 8eede11..2b610c0 100644
--- a/src/js/error.mbt
+++ b/src/js/error.mbt
@@ -9,7 +9,7 @@ pub fn Error_::cause(self : Error_) -> Value? {
   let Error_(inner) = self
   let cause = Error_::cause_ffi(inner)
   guard not(cause.is_undefined()) else { None }
-  Some(cause.cast())
+  Some(cause.unsafe_into())
 }
 
 ///|
@@ -33,7 +33,7 @@ extern "js" fn Error_::wrap_ffi(
 ///|
 pub fn Error_::wrap[T](
   op : () -> Value,
-  map_ok~ : (Value) -> T = Value::cast
+  map_ok~ : (Value) -> T = Value::unsafe_into
 ) -> T!Error_ {
   let mut res : Result[Value, Error_] = Ok(Value::undefined())
   Error_::wrap_ffi(op, fn(v) { res = Ok(v) }, fn(e) { res = Err(Error_(e)) })
diff --git a/src/js/js.mbti b/src/js/js.mbti
index 5ab1fcd..c90410e 100644
--- a/src/js/js.mbti
+++ b/src/js/js.mbti
@@ -64,10 +64,13 @@ impl Show for Error_
 type Nullable[_]
 impl Nullable {
   from_option[T](T?) -> Self[T]
+  #deprecated
   get_exn[T](Self[T]) -> T
   is_null[T](Self[T]) -> Bool
   null[T]() -> Self[T]
   to_option[T](Self[T]) -> T?
+  unsafe_get[T](Self[T]) -> T
+  unwrap[T](Self[T]) -> T
 }
 
 pub type Object Value
@@ -88,10 +91,13 @@ impl Object {
 type Optional[_]
 impl Optional {
   from_option[T](T?) -> Self[T]
+  #deprecated
   get_exn[T](Self[T]) -> T
   is_undefined[T](Self[T]) -> Bool
   to_option[T](Self[T]) -> T?
   undefined[T]() -> Self[T]
+  unsafe_get[T](Self[T]) -> T
+  unwrap[T](Self[T]) -> T
 }
 
 pub extern type Promise
@@ -215,14 +221,18 @@ impl Value {
   apply_with_index[Arg, Result](Self, Int, Array[Arg]) -> Result
   apply_with_string[Arg, Result](Self, String, Array[Arg]) -> Result
   apply_with_symbol[Arg, Result](Self, Symbol, Array[Arg]) -> Result
+  #deprecated
   cast[T](Self) -> T
+  #deprecated
   cast_from[T](T) -> Self
   extends(Self, Self) -> Self
+  from[T](T) -> Self
   from_json(Json) -> Self!
   from_json_string(String) -> Self!
   get_with_index[T](Self, Int) -> T
   get_with_string[T](Self, String) -> T
   get_with_symbol[T](Self, Symbol) -> T
+  into[T](Self) -> T
   is_bool(Self) -> Bool
   is_null(Self) -> Bool
   is_number(Self) -> Bool
@@ -240,6 +250,7 @@ impl Value {
   to_json(Self) -> Json!
   to_json_string(Self) -> String!
   to_string(Self) -> String
+  unsafe_into[T](Self) -> T
 }
 impl Show for Value
 impl @moonbitlang/core/json.FromJson for Value
diff --git a/src/js/null.mbt b/src/js/null.mbt
index 59b44e7..d13b7c1 100644
--- a/src/js/null.mbt
+++ b/src/js/null.mbt
@@ -3,24 +3,41 @@ extern type Nullable[_]
 
 ///|
 pub fn Nullable::is_null[T](self : Nullable[T]) -> Bool {
-  Value::is_null(Value::cast_from(self))
+  Value::is_null(Value::from(self))
 }
 
 ///|
+#deprecated("get_exn is not null-safety. Use `unwrap` or `unsafe_get` instead.")
 pub fn Nullable::get_exn[T](self : Nullable[T]) -> T = "%identity"
 
-///|
+///| Get the underlying value without checking for null.
+/// 
+/// This is unsafe and should only be used when you are sure that the value is not null.
+/// It's recommended to use `unwrap` instead.
+pub fn Nullable::unsafe_get[T](self : Nullable[T]) -> T = "%identity"
+
+///| Get the underlying value with checking for null.
+/// 
+/// If the value is null, it will abort the program.
+pub fn Nullable::unwrap[T](self : Nullable[T]) -> T {
+  if self.is_null() {
+    abort("unwrap on null")
+  }
+  self.unsafe_get()
+}
+
+///| Convert a Nullable value to an Option.
 pub fn Nullable::to_option[T](self : Nullable[T]) -> T? {
-  guard not(Value::cast_from(self).is_null()) else { None }
-  Some(self.get_exn())
+  guard not(Value::from(self).is_null()) else { None }
+  Some(self.unsafe_get())
 }
 
 ///|
 pub fn Nullable::null[T]() -> Nullable[T] {
-  Value::null().cast()
+  Value::null().unsafe_into()
 }
 
 ///|
 pub fn Nullable::from_option[T](value : T?) -> Nullable[T] {
-  value.map(Value::cast_from).or_else(Value::null).cast()
+  value.map(Value::from).or_else(Value::null).unsafe_into()
 }
diff --git a/src/js/object.mbt b/src/js/object.mbt
index 83062bc..5936801 100644
--- a/src/js/object.mbt
+++ b/src/js/object.mbt
@@ -48,10 +48,10 @@ pub fn Object::from_iter2[K, V](it : Iter2[K, V]) -> Object {
 
 ///|
 pub fn Object::op_get[K, V](self : Object, key : K) -> V {
-  self._.get_ffi(Value::cast_from(key)).cast()
+  self._.get_ffi(Value::from(key)).unsafe_into()
 }
 
 ///|
 pub fn Object::op_set[K, V](self : Object, key : K, value : V) -> Unit {
-  self._.set_ffi(Value::cast_from(key), Value::cast_from(value))
+  self._.set_ffi(Value::from(key), Value::from(value))
 }
diff --git a/src/js/optional.mbt b/src/js/optional.mbt
index 767085d..38ede0f 100644
--- a/src/js/optional.mbt
+++ b/src/js/optional.mbt
@@ -3,30 +3,44 @@ extern type Optional[_]
 
 ///|
 pub fn Optional::is_undefined[T](self : Optional[T]) -> Bool {
-  self |> Value::cast_from |> Value::is_undefined
+  self |> Value::from |> Value::is_undefined
 }
 
-///|
+///| 
+#deprecated("get_exn is not undefined-safety. Use `unwrap` or `to_option` instead.")
 pub fn Optional::get_exn[T](self : Optional[T]) -> T = "%identity"
 
-///|
+///| Get the underlying value without checking for undefined.
+pub fn Optional::unsafe_get[T](self : Optional[T]) -> T = "%identity"
+
+///| Get the underlying value with checking for undefined.
+/// 
+/// If the value is undefined, it will abort the program.
+pub fn Optional::unwrap[T](self : Optional[T]) -> T {
+  if self.is_undefined() {
+    abort("unwrap on undefined")
+  }
+  self.unsafe_get()
+}
+
+///| Convert an Optional value to an Option.
 pub fn Optional::to_option[T](self : Optional[T]) -> T? {
-  if Value::cast_from(self).is_undefined() {
+  if Value::from(self).is_undefined() {
     None
   } else {
-    Some(self.get_exn())
+    Some(self.unsafe_get())
   }
 }
 
 ///|
 pub fn Optional::undefined[T]() -> Optional[T] {
-  Value::undefined().cast()
+  Value::undefined().unsafe_into()
 }
 
 ///|
 pub fn Optional::from_option[T](value : T?) -> Optional[T] {
   match value {
-    Some(v) => Value::cast_from(v).cast()
+    Some(v) => Value::from(v).unsafe_into()
     None => Optional::undefined()
   }
 }
diff --git a/src/js/require.mbt b/src/js/require.mbt
index 8a4479e..8ad369d 100644
--- a/src/js/require.mbt
+++ b/src/js/require.mbt
@@ -4,6 +4,6 @@ extern "js" fn require_ffi(path : String) -> Value = "(path) => require(path)"
 ///|
 pub fn require(path : String, keys~ : Array[String] = []) -> Value {
   keys.fold(init=require_ffi(path), fn {
-    acc, key => get_ffi(acc, Value::cast_from(key))
+    acc, key => get_ffi(acc, Value::from(key))
   })
 }
diff --git a/src/js/symbol.mbt b/src/js/symbol.mbt
index f4fd347..262eaf8 100644
--- a/src/js/symbol.mbt
+++ b/src/js/symbol.mbt
@@ -3,12 +3,12 @@ extern type Symbol
 
 ///|
 pub fn Symbol::make() -> Symbol {
-  Symbol::make_ffi(Value::undefined()).cast()
+  Symbol::make_ffi(Value::undefined()).unsafe_into()
 }
 
 ///|
 pub fn Symbol::make_with_string_js(value : String) -> Symbol {
-  Symbol::make_ffi(Value::cast_from(value)).cast()
+  Symbol::make_ffi(Value::from(value)).unsafe_into()
 }
 
 ///|
@@ -18,7 +18,7 @@ pub fn Symbol::make_with_string(value : String) -> Symbol {
 
 ///|
 pub fn Symbol::make_with_number(num : Double) -> Symbol {
-  Symbol::make_ffi(Value::cast_from(num)).cast()
+  Symbol::make_ffi(Value::from(num)).unsafe_into()
 }
 
 ///|
@@ -30,11 +30,11 @@ extern "js" fn Symbol::iterator_ffi() -> Value =
   #| () => Symbol.iterator
 
 ///|
-pub let iterator : Symbol = Symbol::iterator_ffi().cast()
+pub let iterator : Symbol = Symbol::iterator_ffi().unsafe_into()
 
 ///|
 extern "js" fn Symbol::async_iterator_ffi() -> Value =
   #| () => Symbol.asyncIterator
 
 ///|
-pub let async_iterator : Symbol = Symbol::async_iterator_ffi().cast()
+pub let async_iterator : Symbol = Symbol::async_iterator_ffi().unsafe_into()
diff --git a/src/js/union.mbt b/src/js/union.mbt
index a0cd86a..0f29281 100644
--- a/src/js/union.mbt
+++ b/src/js/union.mbt
@@ -3,22 +3,22 @@ extern type Union2[_, _]
 
 ///|
 pub fn Union2::to0[A : Cast, B](self : Union2[A, B]) -> A? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union2::to1[A, B : Cast](self : Union2[A, B]) -> B? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union2::from0[A : Cast, B](value : A) -> Union2[A, B] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union2::from1[A, B : Cast](value : B) -> Union2[A, B] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///| Union type `A | B | C` for JavaScript values.
@@ -26,32 +26,32 @@ extern type Union3[_, _, _]
 
 ///|
 pub fn Union3::to0[A : Cast, B, C](self : Union3[A, B, C]) -> A? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union3::to1[A, B : Cast, C](self : Union3[A, B, C]) -> B? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union3::to2[A, B, C : Cast](self : Union3[A, B, C]) -> C? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union3::from0[A : Cast, B, C](value : A) -> Union3[A, B, C] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union3::from1[A, B : Cast, C](value : B) -> Union3[A, B, C] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union3::from2[A, B, C : Cast](value : C) -> Union3[A, B, C] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///| Union type `A | B | C | D` for JavaScript values.
@@ -59,42 +59,42 @@ extern type Union4[_, _, _, _]
 
 ///|
 pub fn Union4::to0[A : Cast, B, C, D](self : Union4[A, B, C, D]) -> A? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union4::to1[A, B : Cast, C, D](self : Union4[A, B, C, D]) -> B? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union4::to2[A, B, C : Cast, D](self : Union4[A, B, C, D]) -> C? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union4::to3[A, B, C, D : Cast](self : Union4[A, B, C, D]) -> D? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union4::from0[A : Cast, B, C, D](value : A) -> Union4[A, B, C, D] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union4::from1[A, B : Cast, C, D](value : B) -> Union4[A, B, C, D] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union4::from2[A, B, C : Cast, D](value : C) -> Union4[A, B, C, D] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union4::from3[A, B, C, D : Cast](value : D) -> Union4[A, B, C, D] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///| Union type `A | B | C | D | E` for JavaScript values.
@@ -102,52 +102,52 @@ extern type Union5[_, _, _, _, _]
 
 ///|
 pub fn Union5::to0[A : Cast, B, C, D, E](self : Union5[A, B, C, D, E]) -> A? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union5::to1[A, B : Cast, C, D, E](self : Union5[A, B, C, D, E]) -> B? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union5::to2[A, B, C : Cast, D, E](self : Union5[A, B, C, D, E]) -> C? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union5::to3[A, B, C, D : Cast, E](self : Union5[A, B, C, D, E]) -> D? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union5::to4[A, B, C, D, E : Cast](self : Union5[A, B, C, D, E]) -> E? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union5::from0[A : Cast, B, C, D, E](value : A) -> Union5[A, B, C, D, E] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union5::from1[A, B : Cast, C, D, E](value : B) -> Union5[A, B, C, D, E] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union5::from2[A, B, C : Cast, D, E](value : C) -> Union5[A, B, C, D, E] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union5::from3[A, B, C, D : Cast, E](value : D) -> Union5[A, B, C, D, E] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union5::from4[A, B, C, D, E : Cast](value : E) -> Union5[A, B, C, D, E] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///| Union type `A | B | C | D | E | F` for JavaScript values.
@@ -157,84 +157,84 @@ extern type Union6[_, _, _, _, _, _]
 pub fn Union6::to0[A : Cast, B, C, D, E, F](
   self : Union6[A, B, C, D, E, F]
 ) -> A? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union6::to1[A, B : Cast, C, D, E, F](
   self : Union6[A, B, C, D, E, F]
 ) -> B? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union6::to2[A, B, C : Cast, D, E, F](
   self : Union6[A, B, C, D, E, F]
 ) -> C? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union6::to3[A, B, C, D : Cast, E, F](
   self : Union6[A, B, C, D, E, F]
 ) -> D? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union6::to4[A, B, C, D, E : Cast, F](
   self : Union6[A, B, C, D, E, F]
 ) -> E? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union6::to5[A, B, C, D, E, F : Cast](
   self : Union6[A, B, C, D, E, F]
 ) -> F? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union6::from0[A : Cast, B, C, D, E, F](
   value : A
 ) -> Union6[A, B, C, D, E, F] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union6::from1[A, B : Cast, C, D, E, F](
   value : B
 ) -> Union6[A, B, C, D, E, F] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union6::from2[A, B, C : Cast, D, E, F](
   value : C
 ) -> Union6[A, B, C, D, E, F] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union6::from3[A, B, C, D : Cast, E, F](
   value : D
 ) -> Union6[A, B, C, D, E, F] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union6::from4[A, B, C, D, E : Cast, F](
   value : E
 ) -> Union6[A, B, C, D, E, F] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union6::from5[A, B, C, D, E, F : Cast](
   value : F
 ) -> Union6[A, B, C, D, E, F] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///| Union type `A | B | C | D | E | F | G` for JavaScript values.
@@ -244,98 +244,98 @@ extern type Union7[_, _, _, _, _, _, _]
 pub fn Union7::to0[A : Cast, B, C, D, E, F, G](
   self : Union7[A, B, C, D, E, F, G]
 ) -> A? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union7::to1[A, B : Cast, C, D, E, F, G](
   self : Union7[A, B, C, D, E, F, G]
 ) -> B? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union7::to2[A, B, C : Cast, D, E, F, G](
   self : Union7[A, B, C, D, E, F, G]
 ) -> C? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union7::to3[A, B, C, D : Cast, E, F, G](
   self : Union7[A, B, C, D, E, F, G]
 ) -> D? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union7::to4[A, B, C, D, E : Cast, F, G](
   self : Union7[A, B, C, D, E, F, G]
 ) -> E? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union7::to5[A, B, C, D, E, F : Cast, G](
   self : Union7[A, B, C, D, E, F, G]
 ) -> F? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union7::to6[A, B, C, D, E, F, G : Cast](
   self : Union7[A, B, C, D, E, F, G]
 ) -> G? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union7::from0[A : Cast, B, C, D, E, F, G](
   value : A
 ) -> Union7[A, B, C, D, E, F, G] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union7::from1[A, B : Cast, C, D, E, F, G](
   value : B
 ) -> Union7[A, B, C, D, E, F, G] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union7::from2[A, B, C : Cast, D, E, F, G](
   value : C
 ) -> Union7[A, B, C, D, E, F, G] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union7::from3[A, B, C, D : Cast, E, F, G](
   value : D
 ) -> Union7[A, B, C, D, E, F, G] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union7::from4[A, B, C, D, E : Cast, F, G](
   value : E
 ) -> Union7[A, B, C, D, E, F, G] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union7::from5[A, B, C, D, E, F : Cast, G](
   value : F
 ) -> Union7[A, B, C, D, E, F, G] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union7::from6[A, B, C, D, E, F, G : Cast](
   value : G
 ) -> Union7[A, B, C, D, E, F, G] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///| Union type `A | B | C | D | E | F | G | H` for JavaScript values.
@@ -345,110 +345,110 @@ extern type Union8[_, _, _, _, _, _, _, _]
 pub fn Union8::to0[A : Cast, B, C, D, E, F, G, H](
   self : Union8[A, B, C, D, E, F, G, H]
 ) -> A? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union8::to1[A, B : Cast, C, D, E, F, G, H](
   self : Union8[A, B, C, D, E, F, G, H]
 ) -> B? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union8::to2[A, B, C : Cast, D, E, F, G, H](
   self : Union8[A, B, C, D, E, F, G, H]
 ) -> C? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union8::to3[A, B, C, D : Cast, E, F, G, H](
   self : Union8[A, B, C, D, E, F, G, H]
 ) -> D? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union8::to4[A, B, C, D, E : Cast, F, G, H](
   self : Union8[A, B, C, D, E, F, G, H]
 ) -> E? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union8::to5[A, B, C, D, E, F : Cast, G, H](
   self : Union8[A, B, C, D, E, F, G, H]
 ) -> F? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union8::to6[A, B, C, D, E, F, G : Cast, H](
   self : Union8[A, B, C, D, E, F, G, H]
 ) -> G? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union8::to7[A, B, C, D, E, F, G, H : Cast](
   self : Union8[A, B, C, D, E, F, G, H]
 ) -> H? {
-  Cast::into(Value::cast_from(self))
+  Cast::into(Value::from(self))
 }
 
 ///|
 pub fn Union8::from0[A : Cast, B, C, D, E, F, G, H](
   value : A
 ) -> Union8[A, B, C, D, E, F, G, H] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union8::from1[A, B : Cast, C, D, E, F, G, H](
   value : B
 ) -> Union8[A, B, C, D, E, F, G, H] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union8::from2[A, B, C : Cast, D, E, F, G, H](
   value : C
 ) -> Union8[A, B, C, D, E, F, G, H] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union8::from3[A, B, C, D : Cast, E, F, G, H](
   value : D
 ) -> Union8[A, B, C, D, E, F, G, H] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union8::from4[A, B, C, D, E : Cast, F, G, H](
   value : E
 ) -> Union8[A, B, C, D, E, F, G, H] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union8::from5[A, B, C, D, E, F : Cast, G, H](
   value : F
 ) -> Union8[A, B, C, D, E, F, G, H] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union8::from6[A, B, C, D, E, F, G : Cast, H](
   value : G
 ) -> Union8[A, B, C, D, E, F, G, H] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
 
 ///|
 pub fn Union8::from7[A, B, C, D, E, F, G, H : Cast](
   value : H
 ) -> Union8[A, B, C, D, E, F, G, H] {
-  Cast::from(value).cast()
+  Cast::from(value).unsafe_into()
 }
diff --git a/src/js/value.mbt b/src/js/value.mbt
index 244eeaa..1d69973 100644
--- a/src/js/value.mbt
+++ b/src/js/value.mbt
@@ -2,11 +2,32 @@
 pub extern type Value
 
 ///|
+#deprecated("Use `Value::from` instead.")
 pub fn Value::cast_from[T](value : T) -> Value = "%identity"
 
-///|
+///| 
+#deprecated("Use `Value::into` or `Value::unsafe_into` instead.")
 pub fn Value::cast[T](self : Value) -> T = "%identity"
 
+///| Create a `Value` from any type, checking for null or undefined.
+pub fn Value::from[T](self : T) -> Value = "%identity"
+
+///| Cast a `Value` to any type, without checking for null or undefined.
+pub fn Value::unsafe_into[T](self : Value) -> T = "%identity"
+
+///| Convert a `Value` to any type, checking for null or undefined.
+/// 
+/// If the value is null or undefined, it will abort the program.
+pub fn Value::into[T](self : Value) -> T {
+  if self.is_null() {
+    abort("Value::cast on null")
+  }
+  if self.is_undefined() {
+    abort("Value::cast on undefined")
+  }
+  self.unsafe_into()
+}
+
 ///|
 pub extern "js" fn Value::to_string(self : Value) -> String = "(self) => self.toString()"
 
@@ -20,38 +41,38 @@ pub let globalThis : Value = get_globalThis()
 
 ///|
 pub fn get_with_string[T](self : Value, key : String) -> T {
-  self.get_ffi(Value::cast_from(key)).cast()
+  self.get_ffi(Value::from(key)).unsafe_into()
 }
 
 ///|
 pub fn get_with_symbol[T](self : Value, key : Symbol) -> T {
-  self.get_ffi(Value::cast_from(key)).cast()
+  self.get_ffi(Value::from(key)).unsafe_into()
 }
 
 ///|
 pub fn get_with_index[T](self : Value, index : Int) -> T {
-  self.get_ffi(Value::cast_from(index)).cast()
+  self.get_ffi(Value::from(index)).unsafe_into()
 }
 
 ///|
 pub fn set_with_string[T](self : Value, key : String, value : T) -> Unit {
-  self.set_ffi(Value::cast_from(key), Value::cast_from(value))
+  self.set_ffi(Value::from(key), Value::from(value))
 }
 
 ///|
 pub fn set_with_symbol[T](self : Value, key : Symbol, value : T) -> Unit {
-  self.set_ffi(Value::cast_from(key), Value::cast_from(value))
+  self.set_ffi(Value::from(key), Value::from(value))
 }
 
 ///|
 pub fn set_with_index[T](self : Value, index : Int, value : T) -> Unit {
-  self.set_ffi(Value::cast_from(index), Value::cast_from(value))
+  self.set_ffi(Value::from(index), Value::from(value))
 }
 
 ///|
 /// `self(...args)`
 pub fn Value::apply[Arg, Result](self : Value, args : Array[Arg]) -> Result {
-  self.apply_self_ffi(Value::cast_from(args)).cast()
+  self.apply_self_ffi(Value::from(args)).unsafe_into()
 }
 
 ///|
@@ -61,7 +82,7 @@ pub fn Value::apply_with_string[Arg, Result](
   key : String,
   args : Array[Arg]
 ) -> Result {
-  self.apply_ffi(Value::cast_from(key), Value::cast_from(args)).cast()
+  self.apply_ffi(Value::from(key), Value::from(args)).unsafe_into()
 }
 
 ///|
@@ -71,7 +92,7 @@ pub fn Value::apply_with_symbol[Arg, Result](
   key : Symbol,
   args : Array[Arg]
 ) -> Result {
-  self.apply_ffi(Value::cast_from(key), Value::cast_from(args)).cast()
+  self.apply_ffi(Value::from(key), Value::from(args)).unsafe_into()
 }
 
 ///|
@@ -81,13 +102,13 @@ pub fn Value::apply_with_index[Arg, Result](
   index : Int,
   args : Array[Arg]
 ) -> Result {
-  self.apply_ffi(Value::cast_from(index), Value::cast_from(args)).cast()
+  self.apply_ffi(Value::from(index), Value::from(args)).unsafe_into()
 }
 
 ///|
 /// `new self(...args)`
 pub fn Value::new[Arg, Result](self : Value, args : Array[Arg]) -> Result {
-  self.new_self_ffi(Value::cast_from(args)).cast()
+  self.new_self_ffi(Value::from(args)).unsafe_into()
 }
 
 ///|
@@ -97,7 +118,7 @@ pub fn Value::new_with_string[Arg, Result](
   key : String,
   args : Array[Arg]
 ) -> Result {
-  self.new_ffi(Value::cast_from(key), Value::cast_from(args)).cast()
+  self.new_ffi(Value::from(key), Value::from(args)).unsafe_into()
 }
 
 ///|
@@ -107,7 +128,7 @@ pub fn Value::new_with_symbol[Arg, Result](
   key : Symbol,
   args : Array[Arg]
 ) -> Result {
-  self.new_ffi(Value::cast_from(key), Value::cast_from(args)).cast()
+  self.new_ffi(Value::from(key), Value::from(args)).unsafe_into()
 }
 
 ///|
@@ -117,7 +138,7 @@ pub fn Value::new_with_index[Arg, Result](
   index : Int,
   args : Array[Arg]
 ) -> Result {
-  self.new_ffi(Value::cast_from(index), Value::cast_from(args)).cast()
+  self.new_ffi(Value::from(index), Value::from(args)).unsafe_into()
 }
 
 ///|
@@ -128,17 +149,17 @@ pub fn Value::from_json!(json : Json) -> Value {
 ///|
 pub impl @json.FromJson for Value with from_json(json : Json, path) {
   match json {
-    String(s) => Value::cast_from(s)
-    Number(n) => Value::cast_from(n)
-    False => Value::cast_from(false)
-    True => Value::cast_from(true)
+    String(s) => Value::from(s)
+    Number(n) => Value::from(n)
+    False => Value::from(false)
+    True => Value::from(true)
     Null => Value::null()
     Array(xs) => {
       let acc = Array::new(capacity=xs.length())
       for x in xs {
         acc.push((@json.from_json!(x, path~) : Value))
       }
-      Value::cast_from(acc)
+      Value::from(acc)
     }
     Object(kvs) => {
       let acc = Object::new()