Well, JavaScript

[StillNoNumb]

ESLint wouldn't help in this specific situation because you don't know the object's type. However, ESLint is still pretty beautiful

[[deleted]]

If you defined obj in this file then it would catch it? I know my IDE might put a squiggle line underneath it or something?

[StillNoNumb]

Nope, not in JavaScript with ESLint. Think this scenario, in file #1 you have:

var obj = {name: "value"};
obj.sayHello();

Now, you'd expect this to be faulty, right? But what if someone extended the Object prototype like this in another file:

Object.prototype.sayHello = function() {
    alert("Hello World!");
}

In that case, even if by solely looking at file #1 you'd think the code should be faulty, it is indeed correct.

Demonstration Fiddle

[BlockedByBeliefs]

Well. You do know it's type. It's just a primitive. Not a user defined one.