Add Error.isError (#682)

It's strictly speaking not at phase 3 yet (almost!) but it's very easy
to implement and quite useful.

Author: bnoordhuis

quickjs.c

@@ -37928,6 +37928,12 @@ static const JSCFunctionListEntry js_error_proto_funcs[] = {
     JS_PROP_STRING_DEF("message", "", JS_PROP_WRITABLE | JS_PROP_CONFIGURABLE ),
 };
 
+static JSValue js_error_isError(JSContext *ctx, JSValue this_val,
+                                int argc, JSValue *argv)
+{
+    return js_bool(JS_IsError(ctx, argv[0]));
+}
+
 static JSValue js_error_get_stackTraceLimit(JSContext *ctx, JSValue this_val)
 {
     JSValue val;
@@ -37971,6 +37977,7 @@ static JSValue js_error_set_prepareStackTrace(JSContext *ctx, JSValue this_val,
 }
 
 static const JSCFunctionListEntry js_error_funcs[] = {
+    JS_CFUNC_DEF("isError", 1, js_error_isError ),
     JS_CGETSET_DEF("stackTraceLimit", js_error_get_stackTraceLimit, js_error_set_stackTraceLimit ),
     JS_CGETSET_DEF("prepareStackTrace", js_error_get_prepareStackTrace, js_error_set_prepareStackTrace ),
 };

test262.conf

@@ -97,7 +97,7 @@ destructuring-assignment
 destructuring-binding
 dynamic-import
 error-cause
-Error.isError=skip
+Error.isError
 explicit-resource-management=skip
 exponentiation
 export-star-as-namespace-from-module