Keeping only certain properties in a JavaScript object

Question

I have an object. I would like to modify the object (not clone it) by removing all properties except for certain specific properties. For instance, if I started with this o

Answer 1

Just re-initialise the object:

myObj = {
    p1:   myObj.p1,
    p2:   myObj.p2,
    p100: myObj.p100
};

Another way is to delete certain properties, which is less effective:

var prop = ['p1', 'p2', 'p100'];
for (var k in myObj) {
    if (prop.indexOf(k) < 0) {
        delete myObj[k];
    }
}