Change JSClosure.release to deinit

IntegrationTests/TestSuites/Sources/PrimaryTests/main.swift

@@ -331,6 +331,22 @@ ObjectRef_Lifetime: do {
     let ref2 = identity(ref1).object!
     try expectEqual(ref1.prop_2, .number(2))
     try expectEqual(ref2.prop_2, .number(2))
+    identity.release()
+} catch {
+    print(error)
+}
+
+func closureScope() -> ObjectIdentifier {
+    let closure = JSClosure { _ in .undefined }
+    let result = ObjectIdentifier(closure)
+    closure.release()
+    return result
+}
+
+Closure_Identifiers: do {
+    let oid1 = closureScope()
+    let oid2 = closureScope()
+    try expectEqual(oid1, oid2)
 } catch {
     print(error)
 }

Sources/JavaScriptKit/JSFunction.swift

@@ -68,6 +68,8 @@ public class JSClosure: JSFunctionRef {
 
     private var hostFuncRef: JavaScriptHostFuncRef = 0
 
+    private var isReleased = false
+
     public init(_ body: @escaping ([JSValue]) -> JSValue) {
         super.init(id: 0)
         let objectId = ObjectIdentifier(self)
@@ -83,6 +85,16 @@ public class JSClosure: JSFunctionRef {
 
     public func release() {
         Self.sharedFunctions[hostFuncRef] = nil
+        isReleased = true
+    }
+
+    deinit {
+        guard isReleased else {
+            fatalError("""
+            release() must be called on closures manually before deallocating.
+            This is caused by the lack of support for the `FinalizationRegistry` API in Safari.
+            """)
+        }
     }
 }