2 files changed, 47 insertions, 4 deletions
diff --git a/serde_v8/ser.rs b/serde_v8/ser.rs
index 0c6c52da0..31d3e3144 100644
--- a/serde_v8/ser.rs
+++ b/serde_v8/ser.rs
@@ -377,6 +377,9 @@ macro_rules! forward_to {
     };
 }
 
+const MAX_SAFE_INTEGER: i64 = (1 << 53) - 1;
+const MIN_SAFE_INTEGER: i64 = -MAX_SAFE_INTEGER;
+
 impl<'a, 'b, 'c> ser::Serializer for Serializer<'a, 'b, 'c> {
   type Ok = v8::Local<'a, v8::Value>;
   type Error = Error;
@@ -399,8 +402,6 @@ impl<'a, 'b, 'c> ser::Serializer for Serializer<'a, 'b, 'c> {
       serialize_u16(u16, serialize_u32, 'a);
 
       serialize_f32(f32, serialize_f64, 'a);
-      serialize_u64(u64, serialize_f64, 'a);
-      serialize_i64(i64, serialize_f64, 'a);
   }
 
   fn serialize_i32(self, v: i32) -> JsResult<'a> {
@@ -411,6 +412,28 @@ impl<'a, 'b, 'c> ser::Serializer for Serializer<'a, 'b, 'c> {
     Ok(v8::Integer::new_from_unsigned(&mut self.scope.borrow_mut(), v).into())
   }
 
+  fn serialize_i64(self, v: i64) -> JsResult<'a> {
+    let s = &mut self.scope.borrow_mut();
+    // If i64 can fit in max safe integer bounds then serialize as v8::Number
+    // otherwise serialize as v8::BigInt
+    if (MIN_SAFE_INTEGER..=MAX_SAFE_INTEGER).contains(&v) {
+      Ok(v8::Number::new(s, v as _).into())
+    } else {
+      Ok(v8::BigInt::new_from_i64(s, v).into())
+    }
+  }
+
+  fn serialize_u64(self, v: u64) -> JsResult<'a> {
+    let s = &mut self.scope.borrow_mut();
+    // If u64 can fit in max safe integer bounds then serialize as v8::Number
+    // otherwise serialize as v8::BigInt
+    if v <= (MAX_SAFE_INTEGER as u64) {
+      Ok(v8::Number::new(s, v as _).into())
+    } else {
+      Ok(v8::BigInt::new_from_u64(s, v).into())
+    }
+  }
+
   fn serialize_f64(self, v: f64) -> JsResult<'a> {
     Ok(v8::Number::new(&mut self.scope.borrow_mut(), v).into())
   }
diff --git a/serde_v8/tests/ser.rs b/serde_v8/tests/ser.rs
index 76a43bdcc..0d8d42fe6 100644
--- a/serde_v8/tests/ser.rs
+++ b/serde_v8/tests/ser.rs
@@ -109,7 +109,13 @@ sertest!(ser_option_some, Some(true), "x === true");
 sertest!(ser_option_null, None as Option<bool>, "x === null");
 sertest!(ser_unit_null, (), "x === null");
 sertest!(ser_bool, true, "x === true");
-sertest!(ser_u64, 32, "x === 32");
+sertest!(ser_u64, 9007199254740991_u64, "x === 9007199254740991");
+sertest!(ser_big_int, 9007199254740992_i64, "x === 9007199254740992n");
+sertest!(
+  ser_neg_big_int,
+  -9007199254740992_i64,
+  "x === -9007199254740992n"
+);
 sertest!(ser_f64, 12345.0, "x === 12345.0");
 sertest!(ser_string, "Hello", "x === 'Hello'");
 sertest!(ser_bytes, b"\x01\x02\x03", "arrEqual(x, [1, 2, 3])");
@@ -145,7 +151,21 @@ sertest!(
 ////
 sertest!(ser_json_bool, json!(true), "x === true");
 sertest!(ser_json_null, json!(null), "x === null");
-sertest!(ser_json_int, json!(123), "x === 123");
+sertest!(
+  ser_json_int,
+  json!(9007199254740991_u64),
+  "x === 9007199254740991"
+);
+sertest!(
+  ser_json_big_int,
+  json!(9007199254740992_i64),
+  "x === 9007199254740992n"
+);
+sertest!(
+  ser_json_neg_big_int,
+  json!(-9007199254740992_i64),
+  "x === -9007199254740992n"
+);
 sertest!(ser_json_f64, json!(123.45), "x === 123.45");
 sertest!(ser_json_string, json!("Hello World"), "x === 'Hello World'");
 sertest!(ser_json_obj_empty, json!({}), "objEqual(x, {})");