diff --git a/Cargo.lock b/Cargo.lock
index 523f835..a48769a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -79,12 +79,33 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "anyhow"
+version = "1.0.102"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f202df86484c868dbad7eaa557ef785d5c66295e41b460ef922eca0723b842c"
+
 [[package]]
 name = "autocfg"
 version = "1.5.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f2032f911046de80f0a198e0901378627c33f59ea0ac00e363d481118bd70a53"
 
+[[package]]
+name = "bit-set"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "08807e080ed7f9d5433fa9b275196cfc35414f66a0c79d864dc51a0d825231a3"
+dependencies = [
+ "bit-vec",
+]
+
+[[package]]
+name = "bit-vec"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e764a1d40d510daf35e07be9eb06e75770908c27d411ee6c92109c9840eaaf7"
+
 [[package]]
 name = "bitflags"
 version = "2.12.1"
@@ -250,6 +271,12 @@ version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c34f04666d835ff5d62e058c3995147c06f42fe86ff053337632bca83e42702d"
 
+[[package]]
+name = "equivalent"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
+
 [[package]]
 name = "errno"
 version = "0.3.14"
@@ -283,6 +310,43 @@ dependencies = [
  "windows-sys 0.59.0",
 ]
 
+[[package]]
+name = "fnv"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
+
+[[package]]
+name = "foldhash"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9c4f5dac5e15c24eb999c26181a6ca40b39fe946cbe4c263c7209467bc83af2"
+
+[[package]]
+name = "getrandom"
+version = "0.3.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "899def5c37c4fd7b2664648c28120ecec138e4d395b459e5ca34f9cce2dd77fd"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi 5.3.0",
+ "wasip2",
+]
+
+[[package]]
+name = "getrandom"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0de51e6874e94e7bf76d726fc5d13ba782deca734ff60d5bb2fb2607c7406555"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi 6.0.0",
+ "wasip2",
+ "wasip3",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.14.5"
@@ -293,6 +357,15 @@ dependencies = [
  "allocator-api2",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.15.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9229cfe53dfd69f0609a49f65461bd93001ea1ef889cd5529dd176593f5338a1"
+dependencies = [
+ "foldhash",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.17.1"
@@ -317,6 +390,24 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "id-arena"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3d3067d79b975e8844ca9eb072e16b31c3c1c36928edf9c6789548c524d0d954"
+
+[[package]]
+name = "indexmap"
+version = "2.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d466e9454f08e4a911e14806c24e16fba1b4c121d1ea474396f396069cf949d9"
+dependencies = [
+ "equivalent",
+ "hashbrown 0.17.1",
+ "serde",
+ "serde_core",
+]
+
 [[package]]
 name = "is_terminal_polyfill"
 version = "1.70.2"
@@ -329,6 +420,12 @@ version = "1.0.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f42a60cbdf9a97f5d2305f08a87dc4e09308d1276d28c869c684d7777685682"
 
+[[package]]
+name = "leb128fmt"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09edd9e8b54e49e587e4f6295a7d29c3ea94d469cb40ab8ca70b288248a81db2"
+
 [[package]]
 name = "libc"
 version = "0.2.186"
@@ -699,6 +796,7 @@ dependencies = [
  "hashbrown 0.14.5",
  "oxide_compiler",
  "oxide_kernel",
+ "proptest",
 ]
 
 [[package]]
@@ -763,6 +861,25 @@ dependencies = [
  "siphasher",
 ]
 
+[[package]]
+name = "ppv-lite86"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85eae3c4ed2f50dcfe72643da4befc30deadb458a9b590d720cde2f2b1e97da9"
+dependencies = [
+ "zerocopy",
+]
+
+[[package]]
+name = "prettyplease"
+version = "0.2.37"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "479ca8adacdd7ce8f1fb39ce9ecccbfe93a3f1344b3d0d97f20bc0196208f62b"
+dependencies = [
+ "proc-macro2",
+ "syn",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.106"
@@ -772,6 +889,31 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "proptest"
+version = "1.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4b45fcc2344c680f5025fe57779faef368840d0bd1f42f216291f0dc4ace4744"
+dependencies = [
+ "bit-set",
+ "bit-vec",
+ "bitflags",
+ "num-traits",
+ "rand",
+ "rand_chacha",
+ "rand_xorshift",
+ "regex-syntax",
+ "rusty-fork",
+ "tempfile",
+ "unarray",
+]
+
+[[package]]
+name = "quick-error"
+version = "1.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1d01941d82fa2ab50be1e79e6714289dd7cde78eba4c074bc5a4374f650dfe0"
+
 [[package]]
 name = "quote"
 version = "1.0.45"
@@ -781,6 +923,18 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "r-efi"
+version = "5.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "69cdb34c158ceb288df11e18b4bd39de994f6657d83847bdffdbd7f346754b0f"
+
+[[package]]
+name = "r-efi"
+version = "6.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
+
 [[package]]
 name = "radix_trie"
 version = "0.2.1"
@@ -791,6 +945,44 @@ dependencies = [
  "nibble_vec",
 ]
 
+[[package]]
+name = "rand"
+version = "0.9.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "44c5af06bb1b7d3216d91932aed5265164bf384dc89cd6ba05cf59a35f5f76ea"
+dependencies = [
+ "rand_chacha",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d3022b5f1df60f26e1ffddd6c66e8aa15de382ae63b3a0c1bfc0e4d3e3f325cb"
+dependencies = [
+ "ppv-lite86",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.9.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "76afc826de14238e6e8c374ddcc1fa19e374fd8dd986b0d2af0d02377261d83c"
+dependencies = [
+ "getrandom 0.3.4",
+]
+
+[[package]]
+name = "rand_xorshift"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "513962919efc330f829edb2535844d1b912b0fbe2ca165d613e4e8788bb05a5a"
+dependencies = [
+ "rand_core",
+]
+
 [[package]]
 name = "rayon"
 version = "1.12.0"
@@ -820,6 +1012,12 @@ dependencies = [
  "bitflags",
 ]
 
+[[package]]
+name = "regex-syntax"
+version = "0.8.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc897dd8d9e8bd1ed8cdad82b5966c3e0ecae09fb1907d58efaa013543185d0a"
+
 [[package]]
 name = "rustc-hash"
 version = "2.1.2"
@@ -845,6 +1043,18 @@ version = "1.0.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
 
+[[package]]
+name = "rusty-fork"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cc6bf79ff24e648f6da1f8d1f011e9cac26491b619e6b9280f2b47f1774e6ee2"
+dependencies = [
+ "fnv",
+ "quick-error",
+ "tempfile",
+ "wait-timeout",
+]
+
 [[package]]
 name = "rustyline"
 version = "14.0.0"
@@ -879,6 +1089,12 @@ version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "94143f37725109f92c262ed2cf5e59bce7498c01bcc1502d7b9afe439a4e9f49"
 
+[[package]]
+name = "semver"
+version = "1.0.28"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8a7852d02fc848982e0c167ef163aaff9cd91dc640ba85e263cb1ce46fae51cd"
+
 [[package]]
 name = "seq-macro"
 version = "0.3.6"
@@ -968,6 +1184,19 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "tempfile"
+version = "3.27.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32497e9a4c7b38532efcdebeef879707aa9f794296a4f0244f6f69e9bc8574bd"
+dependencies = [
+ "fastrand",
+ "getrandom 0.4.2",
+ "once_cell",
+ "rustix",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "textwrap"
 version = "0.16.2"
@@ -999,6 +1228,12 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "unarray"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eaea85b334db583fe3274d12b4cd1880032beab409c0d774be044d4480ab9a94"
+
 [[package]]
 name = "unicode-id-start"
 version = "1.4.0"
@@ -1035,6 +1270,12 @@ version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b4ac048d71ede7ee76d585517add45da530660ef4390e49b098733c6e897f254"
 
+[[package]]
+name = "unicode-xid"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ebc1c04c71510c7f702b52b7c350734c9ff1295c464a03335b00bb84fc54f853"
+
 [[package]]
 name = "utf8parse"
 version = "0.2.2"
@@ -1047,6 +1288,67 @@ version = "0.9.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
 
+[[package]]
+name = "wait-timeout"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09ac3b126d3914f9849036f826e054cbabdc8519970b8998ddaf3b5bd3c65f11"
+dependencies = [
+ "libc",
+]
+
+[[package]]
+name = "wasip2"
+version = "1.0.3+wasi-0.2.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "20064672db26d7cdc89c7798c48a0fdfac8213434a1186e5ef29fd560ae223d6"
+dependencies = [
+ "wit-bindgen 0.57.1",
+]
+
+[[package]]
+name = "wasip3"
+version = "0.4.0+wasi-0.3.0-rc-2026-01-06"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5428f8bf88ea5ddc08faddef2ac4a67e390b88186c703ce6dbd955e1c145aca5"
+dependencies = [
+ "wit-bindgen 0.51.0",
+]
+
+[[package]]
+name = "wasm-encoder"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "990065f2fe63003fe337b932cfb5e3b80e0b4d0f5ff650e6985b1048f62c8319"
+dependencies = [
+ "leb128fmt",
+ "wasmparser",
+]
+
+[[package]]
+name = "wasm-metadata"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb0e353e6a2fbdc176932bbaab493762eb1255a7900fe0fea1a2f96c296cc909"
+dependencies = [
+ "anyhow",
+ "indexmap",
+ "wasm-encoder",
+ "wasmparser",
+]
+
+[[package]]
+name = "wasmparser"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47b807c72e1bac69382b3a6fb3dbe8ea4c0ed87ff5629b8685ae6b9a611028fe"
+dependencies = [
+ "bitflags",
+ "hashbrown 0.15.5",
+ "indexmap",
+ "semver",
+]
+
 [[package]]
 name = "winapi"
 version = "0.3.9"
@@ -1166,6 +1468,100 @@ version = "0.52.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "589f6da84c646204747d1270a2a5661ea66ed1cced2631d546fdfb155959f9ec"
 
+[[package]]
+name = "wit-bindgen"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d7249219f66ced02969388cf2bb044a09756a083d0fab1e566056b04d9fbcaa5"
+dependencies = [
+ "wit-bindgen-rust-macro",
+]
+
+[[package]]
+name = "wit-bindgen"
+version = "0.57.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1ebf944e87a7c253233ad6766e082e3cd714b5d03812acc24c318f549614536e"
+
+[[package]]
+name = "wit-bindgen-core"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ea61de684c3ea68cb082b7a88508a8b27fcc8b797d738bfc99a82facf1d752dc"
+dependencies = [
+ "anyhow",
+ "heck",
+ "wit-parser",
+]
+
+[[package]]
+name = "wit-bindgen-rust"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b7c566e0f4b284dd6561c786d9cb0142da491f46a9fbed79ea69cdad5db17f21"
+dependencies = [
+ "anyhow",
+ "heck",
+ "indexmap",
+ "prettyplease",
+ "syn",
+ "wasm-metadata",
+ "wit-bindgen-core",
+ "wit-component",
+]
+
+[[package]]
+name = "wit-bindgen-rust-macro"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0c0f9bfd77e6a48eccf51359e3ae77140a7f50b1e2ebfe62422d8afdaffab17a"
+dependencies = [
+ "anyhow",
+ "prettyplease",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "wit-bindgen-core",
+ "wit-bindgen-rust",
+]
+
+[[package]]
+name = "wit-component"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d66ea20e9553b30172b5e831994e35fbde2d165325bec84fc43dbf6f4eb9cb2"
+dependencies = [
+ "anyhow",
+ "bitflags",
+ "indexmap",
+ "log",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "wasm-encoder",
+ "wasm-metadata",
+ "wasmparser",
+ "wit-parser",
+]
+
+[[package]]
+name = "wit-parser"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ecc8ac4bc1dc3381b7f59c34f00b67e18f910c2c0f50015669dde7def656a736"
+dependencies = [
+ "anyhow",
+ "id-arena",
+ "indexmap",
+ "log",
+ "semver",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "unicode-xid",
+ "wasmparser",
+]
+
 [[package]]
 name = "zerocopy"
 version = "0.8.50"
diff --git a/Cargo.toml b/Cargo.toml
index 9c67a16..2511cb3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -31,6 +31,7 @@ dashmap = "6"
 rayon = "1"
 bumpalo = "3"
 hashbrown = "0.14"
+proptest = "1"
 
 [workspace.lints.clippy]
 all = { level = "deny", priority = -1 }
diff --git a/crates/oxide_vm/Cargo.toml b/crates/oxide_vm/Cargo.toml
index db8635e..c329ef2 100644
--- a/crates/oxide_vm/Cargo.toml
+++ b/crates/oxide_vm/Cargo.toml
@@ -11,3 +11,6 @@ oxide_compiler = { path = "../oxide_compiler" }
 oxide_kernel = { path = "../oxide_kernel" }
 bumpalo.workspace = true
 hashbrown.workspace = true
+
+[dev-dependencies]
+proptest.workspace = true
diff --git a/crates/oxide_vm/src/lib.rs b/crates/oxide_vm/src/lib.rs
index 137fb20..523dc41 100644
--- a/crates/oxide_vm/src/lib.rs
+++ b/crates/oxide_vm/src/lib.rs
@@ -1 +1,4 @@
 #![doc = "OxideJS - Register-based VM with epoch arena memory"]
+
+pub mod value;
+pub use value::JsValue;
diff --git a/crates/oxide_vm/src/value.rs b/crates/oxide_vm/src/value.rs
new file mode 100644
index 0000000..006da3a
--- /dev/null
+++ b/crates/oxide_vm/src/value.rs
@@ -0,0 +1,174 @@
+use std::fmt;
+
+/// Quiet NaN prefix — bits 63-51 = sign(1) + exponent(0x7FF) + quiet_bit(1)
+const QNAN_PREFIX: u64 = 0xFFF8_0000_0000_0000;
+
+/// NaN exponent mask — bits 62-52
+const EXP_MASK: u64 = 0x7FF0_0000_0000_0000;
+
+/// Mantissa mask — bits 51-0
+const MANTISSA_MASK: u64 = 0x000F_FFFF_FFFF_FFFF;
+
+/// Tag sits in bits 50-48 of mantissa
+const TAG_MASK: u64 = 0x0007_0000_0000_0000;
+const TAG_SHIFT: u64 = 48;
+const TAG_INT: u64 = 0;
+const TAG_BOOL: u64 = 1;
+const TAG_NULL: u64 = 2;
+const TAG_UNDEFINED: u64 = 3;
+const TAG_OBJECT: u64 = 4;
+
+/// 48-bit pointer mask (x86-64 canonical VA)
+const PTR_MASK: u64 = 0x0000_FFFF_FFFF_FFFF;
+
+/// 32-bit integer payload mask
+const INT_MASK: u64 = 0x0000_0000_FFFF_FFFF;
+
+fn make_tag(tag: u64) -> u64 {
+    QNAN_PREFIX | (tag << TAG_SHIFT)
+}
+
+fn get_tag(bits: u64) -> u64 {
+    (bits & TAG_MASK) >> TAG_SHIFT
+}
+
+#[repr(transparent)]
+#[derive(Copy, Clone, PartialEq)]
+pub struct JsValue(u64);
+
+impl JsValue {
+    pub fn int(v: i32) -> Self {
+        Self(make_tag(TAG_INT) | (v as u32 as u64))
+    }
+
+    pub fn float(v: f64) -> Self {
+        let bits = v.to_bits();
+        if is_nan_bits(bits) {
+            Self(QNAN_PREFIX | 1)
+        } else {
+            Self(bits)
+        }
+    }
+
+    pub fn bool(v: bool) -> Self {
+        Self(make_tag(TAG_BOOL) | (v as u64))
+    }
+
+    pub fn null() -> Self {
+        Self(make_tag(TAG_NULL))
+    }
+
+    pub fn undefined() -> Self {
+        Self(make_tag(TAG_UNDEFINED))
+    }
+
+    pub fn object(ptr: *const u8) -> Self {
+        let addr = ptr as u64;
+        debug_assert!(addr <= PTR_MASK, "object pointer must fit in 48 bits");
+        Self(make_tag(TAG_OBJECT) | addr)
+    }
+
+    pub fn is_double(&self) -> bool {
+        !is_nan_bits(self.0)
+    }
+
+    pub fn is_int(&self) -> bool {
+        get_tag(self.0) == TAG_INT
+    }
+
+    pub fn is_bool(&self) -> bool {
+        get_tag(self.0) == TAG_BOOL
+    }
+
+    pub fn is_null(&self) -> bool {
+        self.0 == make_tag(TAG_NULL)
+    }
+
+    pub fn is_undefined(&self) -> bool {
+        self.0 == make_tag(TAG_UNDEFINED)
+    }
+
+    pub fn is_object(&self) -> bool {
+        get_tag(self.0) == TAG_OBJECT
+    }
+
+    pub fn as_double(&self) -> f64 {
+        debug_assert!(self.is_double(), "JsValue is not a double");
+        f64::from_bits(self.0)
+    }
+
+    pub fn as_int(&self) -> i32 {
+        debug_assert!(self.is_int(), "JsValue is not an int");
+        (self.0 & INT_MASK) as i32
+    }
+
+    pub fn as_bool(&self) -> bool {
+        debug_assert!(self.is_bool(), "JsValue is not a bool");
+        (self.0 & 1) != 0
+    }
+
+    pub fn as_ptr(&self) -> *const u8 {
+        debug_assert!(self.is_object(), "JsValue is not an object");
+        (self.0 & PTR_MASK) as *const u8
+    }
+}
+
+fn is_nan_bits(bits: u64) -> bool {
+    (bits & EXP_MASK) == EXP_MASK && (bits & MANTISSA_MASK) != 0
+}
+
+impl fmt::Display for JsValue {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.is_int() {
+            write!(f, "{}", self.as_int())
+        } else if self.is_double() {
+            let d = self.as_double();
+            if d.is_nan() {
+                write!(f, "NaN")
+            } else if d.is_infinite() {
+                if d.is_sign_positive() {
+                    write!(f, "Infinity")
+                } else {
+                    write!(f, "-Infinity")
+                }
+            } else {
+                write!(f, "{d}")
+            }
+        } else if self.is_bool() {
+            write!(f, "{}", self.as_bool())
+        } else if self.is_null() {
+            write!(f, "null")
+        } else if self.is_undefined() {
+            write!(f, "undefined")
+        } else if self.is_object() {
+            write!(f, "{{object}}")
+        } else {
+            write!(f, "{{unknown}}")
+        }
+    }
+}
+
+impl fmt::Debug for JsValue {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.is_int() {
+            write!(f, "JsValue(Int({}))", self.as_int())
+        } else if self.is_double() {
+            let d = self.as_double();
+            if d.is_nan() {
+                write!(f, "JsValue(Double(NaN))")
+            } else {
+                write!(f, "JsValue(Double({d}))")
+            }
+        } else if self.is_bool() {
+            write!(f, "JsValue(Bool({}))", self.as_bool())
+        } else if self.is_null() {
+            write!(f, "JsValue(Null)")
+        } else if self.is_undefined() {
+            write!(f, "JsValue(Undefined)")
+        } else if self.is_object() {
+            write!(f, "JsValue(Object({:p}))", self.as_ptr())
+        } else {
+            write!(f, "JsValue(Unknown)")
+        }
+    }
+}