Use JS's == operator for JSString equality comparison

Runtime/src/index.ts

@@ -479,6 +479,13 @@ export class SwiftRuntime {
                 return obj instanceof constructor;
             },
 
+            swjs_value_equals: (lhs_ref: ref, rhs_ref: ref) => {
+                const memory = this.memory;
+                const lhs = memory.getObject(lhs_ref);
+                const rhs = memory.getObject(rhs_ref);
+                return lhs == rhs;
+            },
+
             swjs_create_function: (
                 host_func_id: number,
                 line: number,

Runtime/src/types.ts

@@ -96,6 +96,7 @@ export interface ImportedFunctions {
         exception_payload2_ptr: pointer
     ): number;
     swjs_instanceof(obj_ref: ref, constructor_ref: ref): boolean;
+    swjs_value_equals(lhs_ref: ref, rhs_ref: ref): boolean;
     swjs_create_function(host_func_id: number, line: number, file: ref): number;
     swjs_create_typed_array(
         constructor_ref: ref,

Sources/JavaScriptKit/FundamentalObjects/JSString.swift

@@ -77,7 +77,7 @@ public struct JSString: LosslessStringConvertible, Equatable {
     ///   - lhs: A string to compare.
     ///   - rhs: Another string to compare.
     public static func == (lhs: JSString, rhs: JSString) -> Bool {
-        return lhs.guts.buffer == rhs.guts.buffer
+        return swjs_value_equals(lhs.guts.jsRef, rhs.guts.jsRef)
     }
 }
 

Sources/_CJavaScriptKit/include/_CJavaScriptKit.h

@@ -257,6 +257,16 @@ IMPORT_JS_FUNCTION(swjs_call_throwing_new, JavaScriptObjectRef, (const JavaScrip
 IMPORT_JS_FUNCTION(swjs_instanceof, bool, (const JavaScriptObjectRef obj,
                                            const JavaScriptObjectRef constructor))
 
+/// Acts like JavaScript `==` operator.
+/// Performs "==" comparison, a.k.a the "Abstract Equality Comparison"
+/// algorithm defined in the ECMAScript.
+/// https://262.ecma-international.org/11.0/#sec-abstract-equality-comparison
+///
+/// @param lhs The left-hand side value to compare.
+/// @param rhs The right-hand side value to compare.
+/// @result Return `true` if `lhs` is `==` to `rhs`. Return `false` if not.
+IMPORT_JS_FUNCTION(swjs_value_equals, bool, (const JavaScriptObjectRef lhs, const JavaScriptObjectRef rhs))
+
 /// Creates a JavaScript thunk function that calls Swift side closure.
 /// See also comments on JSFunction.swift
 ///

Tests/JavaScriptKitTests/JSStringTests.swift

@@ -0,0 +1,13 @@
+import JavaScriptKit
+import XCTest
+
+final class JSStringTests: XCTestCase {
+    func testEquatable() {
+        let string1 = JSString("Hello, world!")
+        let string2 = JSString("Hello, world!")
+        let string3 = JSString("Hello, world")
+        XCTAssertEqual(string1, string1)
+        XCTAssertEqual(string1, string2)
+        XCTAssertNotEqual(string1, string3)
+    }
+}