Add Hashable conformance to JSObject

IntegrationTests/TestSuites/Sources/PrimaryTests/UnitTestUtils.swift

@@ -38,6 +38,15 @@ func expectEqual<T: Equatable>(
     }
 }
 
+func expectNotEqual<T: Equatable>(
+    _ lhs: T, _ rhs: T,
+    file: StaticString = #file, line: UInt = #line, column: UInt = #column
+) throws {
+    if lhs == rhs {
+        throw MessageError("Expect to not be equal \"\(lhs)\" and \"\(rhs)\"", file: file, line: line, column: column)
+    }
+}
+
 func expectObject(_ value: JSValue, file: StaticString = #file, line: UInt = #line, column: UInt = #column) throws -> JSObject {
     switch value {
     case let .object(ref): return ref

IntegrationTests/TestSuites/Sources/PrimaryTests/main.swift

@@ -746,4 +746,23 @@ try test("Grow Memory") {
     try expectEqual(string, jsString.description)
 }
 
+try test("Hashable Conformance") {
+    let globalObject1 = JSObject.global.console.object!
+    let globalObject2 = JSObject.global.console.object!
+    try expectEqual(globalObject1.hashValue, globalObject2.hashValue)
+    // These are 2 different objects in Swift referencing the same object in JavaScript
+    try expectNotEqual(ObjectIdentifier(globalObject1), ObjectIdentifier(globalObject2))
+
+    let sameObjectSet: Set<JSObject> = [globalObject1, globalObject2]
+    try expectEqual(sameObjectSet.count, 1)
+
+    let objectConstructor = JSObject.global.Object.function!
+    let obj = objectConstructor.new()
+    obj.a = 1.jsValue()
+    let firstHash = obj.hashValue
+    obj.b = 2.jsValue()
+    let secondHash = obj.hashValue
+    try expectEqual(firstHash, secondHash)
+}
+
 Expectation.wait(expectations)

Sources/JavaScriptKit/FundamentalObjects/JSObject.swift

@@ -135,6 +135,16 @@ extension JSObject: CustomStringConvertible {
     public var description: String { self.toString!().string! }
 }
 
+extension JSObject: Hashable {
+    /// Hashes the essential components of this value by feeding them into the
+    /// given hasher.
+    ///
+    /// - Parameter hasher: The hasher to use when combining the components
+    ///   of this instance.
+    public func hash(into hasher: inout Hasher) {
+        hasher.combine(id)
+    }
+}
 
 /// A `JSObject` wrapper that enables throwing method calls capturing `this`.
 /// Exceptions produced by JavaScript functions will be thrown as `JSValue`.