Better way for checking nested object in `if` condition?

Question

Consider I have a object like this:

Obj.Boo.Foo.Zoo

Ok now if I want to be sure that zoo has a value and not empty, I should do:

if(Obj != null && Obj.Boo != null && Obj.Boo.Foo != null && Obj.Boo.Foo.Zoo != null) {
    //blah blah
}

And If I have more nested objects after Zoo, I should expand the if and the code becomes a little bit malformed.

Is there any better way for doing that type of conditions?

Answer 1

I keep a little function I call chainGet(obj, chain, default) around for situations just like this:

function chainGet(obj, chain, dflt) {
    if (typeof chain === "string")
        chain = chain.split(".");
    var result = obj;
    for (var i = 0; i < chain.length; i += 1) {
        if (result === undefined)
            break;
        result = result[chain[i]];
    }
    return result === undefined? dflt : result;
}

For example:

> chainGet({ foo: 42 }, "foo")
42
> chainGet({ foo: 42 }, "bar", "x")
'x'
> chainGet({ foo: { bar: 42 }}), "foo.bar")
42

This even works with arrays:

> chainGet([{ foo: [42] }], [0, "foo", 0])
42

Of course, long chains of dotted accesses are a code smell, so caution should be exercised when using them… but sometimes you've just got to do it ;)