Question

I have the following JavaScript data structure. a[] is an array with text strings as elements. It is not
known in advance what it contains. For example,

a = ["foo", "bar", "baz"...];

res{} is a JSON object with as many keys as elements in “a” with the following rule; the last innermost key of res{} is an object with
an array called features[] or the last innermost key itself is an array. So, if , then res is either

// if
a = ["foo", "bar"];

// then
res = {
    "foo": {
        "bar": {
            "features": []
        }
    }
};

// and I want
data = res["foo"]["bar"].features;

// or
res = {
    "foo": {
        "bar": []
    }
};

// and I want
data = res["foo"]["bar"];

As I said, it is not know in advance how long a[] is or what the values of its elements is. How can I do the above?

Update: fixed a typo in the structure of res

Answer 1

This works ok

function getFeatures(obj, keys) {
  if( keys.length ) {
    key = keys.shift();
    obj = obj[key];
    return getFeatures(obj, keys);
  } else {
    return obj.features || obj;
  }
}

You may want to call it with a copy of the keys-array, as the function shifts elements off of the array it’s passed. I.e.

var keys = ["foo", "bar"];

var res1  = { "foo": { "bar": { "features": [1, 2, 3] } } };
getFeatures(res1, keys.slice(0)); // => [1, 2, 3]

var res2 = { "foo": { "bar": ["a", "b", "c"] } };
getFeatures(res2, keys.slice(0)); // => ["a", "b", "c"]