Improve error messages when calling JavaScript object properties in method style

Author: ledsun

packages/gems/js/lib/js.rb

@@ -173,20 +173,13 @@ def method_missing(sym, *args, &block)
     if sym_str.end_with?("?")
       # When a JS method is called with a ? suffix, it is treated as a predicate method,
       # and the return value is converted to a Ruby boolean value automatically.
-      sym = sym_str[0..-2].to_sym
-      if self[sym].typeof == "function"
-        result = self.call(sym, *args, &block)
-        # Type coerce the result to boolean type
-        # to match the true/false determination in JavaScript's if statement.
-        return JS.global.Boolean(result) == JS::True
-      end
-    end
-
-    if self[sym].typeof == "function"
-      return self.call(sym, *args, &block)
+      result = invoke_js_method(sym_str[0..-2].to_sym, *args, &block)
+      # Type coerce the result to boolean type
+      # to match the true/false determination in JavaScript's if statement.
+      return JS.global.Boolean(result) == JS::True
     end
 
-    super
+    invoke_js_method(sym, *args, &block)
   end
 
   # Check if a JavaScript method exists
@@ -243,6 +236,24 @@ def await
     promise = JS.global[:Promise].resolve(self)
     JS.promise_scheduler.await(promise)
   end
+
+  private
+
+  # Invoke a JavaScript method
+  # If the property of JavaScritp object does not exist, raise a `NoMethodError`.
+  # If the property exists but is not a function, raise a `TypeError`.
+  def invoke_js_method(sym, *args, &block)
+    return self.call(sym, *args, &block) if self[sym].typeof == "function"
+
+    # Check to see if a non-functional property exists.
+    if JS.global[:Reflect].call(:has, self, sym.to_s) == JS::True
+      raise TypeError,
+            "`#{sym}` is not a function. To reference a property, use `[:#{sym}]` syntax instead."
+    end
+
+    raise NoMethodError,
+          "undefined method `#{sym}' for an instance of JS::Object"
+  end
 end
 
 # A wrapper class for JavaScript Error to allow the Error to be thrown in Ruby.

packages/npm-packages/ruby-wasm-wasi/test/unit/test_object.rb

@@ -341,16 +341,27 @@ def test_method_missing_with_property
     object = JS.eval(<<~JS)
       return { property: 42 };
     JS
-    assert_raise(NoMethodError) { object.property }
-    assert_raise(NoMethodError) { object.property? }
+
+    e = assert_raise(TypeError) { object.property }
+    assert_equal "`property` is not a function. To reference a property, use `[:property]` syntax instead.",
+                 e.message
+
+    e = assert_raise(TypeError) { object.property? }
+    assert_equal "`property` is not a function. To reference a property, use `[:property]` syntax instead.",
+                 e.message
   end
 
   def test_method_missing_with_undefined_method
     object = JS.eval(<<~JS)
       return { foo() { return true; } };
     JS
-    assert_raise(NoMethodError) { object.bar }
-    assert_raise(NoMethodError) { object.bar? }
+    e = assert_raise(NoMethodError) { object.bar }
+    assert_equal "undefined method `bar' for an instance of JS::Object",
+                 e.message
+
+    e = assert_raise(NoMethodError) { object.bar? }
+    assert_equal "undefined method `bar' for an instance of JS::Object",
+                 e.message
   end
 
   def test_respond_to_missing?