How to determine whether or not an objects contains a property that points to a specific reference?

Given these two objects:

var object1 = {
    a: function() {},
    b: function() {},
    c: function() {}
};

var object2 = {
    d: function() {},
    e: function() {},
    f: function() {}
};

Here we have two objects each containing 3 properties which are function objects (or, to be precise, references to function objects).

Let's say that f is a reference to one of those 6 function objects. (It was declared like so: var f = object2.e; or var f = objec开发者_C百科t1.c;.)

How can I determine whether or not the reference f is among the 3 references/properties of object1?

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The only thing you can do is to iterate over the object's properties:

var pointsToObject1 = false;

for(var prop in object1) {
    // maybe call hasOwnProperty but I don't think it is necessary here.
    if(f === object1[prop]) {
        pointsToObject1 = true;
        break;
    }
}

f is not really pointing to a property of one of the objects. It is more like both, f and the property, point to the same value/object.

---

So this is my current solution (based on @Felix's answer):

function isIn(r, o) {
    for (var p in o) {
        if ( o.hasOwnProperty(p) ) {
            if ( o[p] === r ) return true;
        }
    }
    return false;
}

And then:

var f = object1.c;

and:

isIn(f, object1) // alerts "true"
isIn(f, object2) // alters "false"

Live demo: http://jsfiddle.net/W3Lub/

What do you think? I find it hard to believe that no browser or library offers this feature?!