Function to look for a key inside a complex object in Javascript

hasKey.js

/**
 * This function allows to search a especific key in a complex object
 * @author orvigas@gmail.com
 * @param (Object) o: Object in which you look for the key
 * @param (string) key: Name of key you're looking for
 * @return (mixed) $r: Return object or value related with key name,
 * instead if key were not found it return undefined
 */

function hasKey(o, key) {
    var $r = void 0;
    Object.keys(o).some(function (k) {
        if (k === key) {
            $r = o[k];
            return true;
        }
        if (o[k] && typeof o[k] === 'object') {
            $r = hasKey(o[k], key);
            return $r !== undefined;
        }
    });
    return $r;
}

/**Example**/
var obj = {
    "prop1": {
        "sprop11": true,
        "sprop12": null
    },
    "prop2": [
        {
            "sprop21": 28,
            "sprop22": [
                {
                    "sprop221": 28,
                    "inner222": [
                        {
                            "stage_id": 28,
                        }
                        , {
                            "deepest": "deepest property"
                        }]
                }]
        }]
};

/** key:prop1 **/
console.log(hasKey(obj, 'prop1'));
/** Output: {"sprop11":true,"sprop12":null} **/

/** key:stage_id **/
console.log(hasKey(obj, 'stage_id'));
/** Output: 28 **/

/** key:deepest **/
console.log(hasKey(obj, 'deepest'));
/** Output: deepest property **/

/** key:non-existent **/
console.log(hasKey(obj, 'non-existent'));
/** Output: undefined **/