question: `isObjectOf()` intended to check prototype properties?

[Milly]

Question

isObjectOf() checks prototype properties. This is intended?

const parent = { a: is.Number };
const child = Object.create(parent);
child.b = is.String;

is.ObjectOf(child)({ a: 0 }); // false
is.ObjectOf(child)({ b: "a" }); // false
is.ObjectOf(child)({ a: 0, b: "a" }); // true

Additional

isStrictOf() does not support this behavior.

is.StrictOf(is.ObjectOf(child))({ a: 0, b: "a" }); // false

Version

v4.0.1 7d8bcbd

[lambdalisue]

No, this is undefined behavior. I haven't considered the use of is.ObjectOf with Object.create.

Are you encountering a specific issue? Since Object.create returns any, the usage you've shown doesn't seem typical.

[Milly]

I am concerned that prototype pollution may result in behavior that developers do not intend.
In other words, if this behavior is not what you intended, I consider it a bug.

(Object.prototype as any).a = is.Number;
is.ObjectOf({ b: is.String })({ b: "a" }); // false
is.ObjectOf({ b: is.String })({ a: 0, b: "a" }); // false

[Milly]

If to fix, the implementation should use Object.keys() instead of for ... in.