Don't throw for non-objects

[Jamesernator]

So a footgun I recently discovered with #field in v is that as it turns out if v is not an object, then #field in v throws an error. While this is consistent with "str" in v, it makes writing a class check even less ergonomic:

function isObject(v) {
    return v !== null && (typeof v === "object" || typeof v === "function");
}

class Point2D {
    static isPoint2D(v) {
        return isObject(v) && #x in v;
    }
    
    #x;
    #y;
    
    // ...
}

It's rather easy to forget to include isObject(v) everytime one writes an SomeClass.isSomeClass method. (Further compounded by the fact one needs to implement isObject in every codebase that does such a check).

This is a great opportunity for class.hasInstance to avoid this issue if it doesn't throw for non-objects:

class Point2D {
    static isPoint2D(v) {
        return class.hasInstance(v);
    }
    
    #x;
    #y;
    
    // ...
}

Point2D.isPoint2D(new Point2D(3, 4)); // true
Point2D.isPoint2D({}); // false
// Doesn't throw, unlike #field in v
Point2D.isPoint2D(3); // false

[ljharb]

v && #x in v seems a bit simpler - it won't throw on non-nullish primitives, so you don't actually need the typeof check - but you're right you need some kind of check.