not a constructor

[Stubbsware]

Speaks for itself, if calling new when its not a constructor, the error being reported is just
TypeError: not a constructor

For example
var Foo = () => {};
var foo = new Foo(); // TypeError: Foo is not a constructor

However, QuickJS just reports
TypeError: not a constructor

[Stubbsware]

Needs verification, but I fixed it for my scenario. Changing line 18814 of quickjs.c from

return JS_ThrowTypeError(ctx, "not a constructor");

to

return JS_ThrowTypeError(ctx, "%s is not a constructor", JS_ToCString(ctx, JS_GetPropertyStr(ctx, func_obj, "name")));

Now running

const Foo = () => {};
const foo = new Foo();

Results in the correct error
TypeError: Foo is not a constructor

[saghul]

Calling JS code to build the error message is likely not a good idea.

In addition you are leaking the C string.

[Stubbsware]

Excellent observation, but i did say I was looking for clarification on if I was on the correct path.

Change:

if (unlikely(!p->is_constructor))
    return JS_ThrowTypeError(ctx, "not a constructor");

To:

if (unlikely(!p->is_constructor)) {
    JSValue name;
    const char *func_name;
    JSValue error;
    name = JS_GetPropertyStr(ctx, func_obj, "name");
    func_name = JS_ToCString(ctx, name);
    error = JS_ThrowTypeError(ctx, "'%s' is not a constructor", func_name);
    JS_FreeCString(ctx, func_name);
    JS_FreeValue(ctx, name);
    return error;
}

[saghul]

The function name can be extracted without calling ToCString, IMHO that would be a better path.

[Stubbsware]

JS_GetPropertyStr returns a JSValue which is not directly represent a string in C. So would need converted with JS_ToCString. If you know something I am missing?

[saghul]

I think using get_func_name, a helper in build_backtrace would be best. It looks for a name property without running JS code.

[richarddd]

@Stubbsware i think @saghul's advice is the path to take. Similarly, not a function can show the function name.