Function that safely navigates javascript object. Original source http://adripofjavascript.com/blog/drips/making-deep-property-access-safe-in-javascript.html

deepGet.js

//If not found returns undefined
function deepGet (obj, properties) {
    // If we have reached an undefined/null property
    // then stop executing and return undefined.
    if (obj === undefined || obj === null) {
        return;
    }

    // If the path array has no more elements, we've reached
    // the intended property and return its value.
    if (properties.length === 0) {
        return obj;
    }

    // Prepare our found property and path array for recursion
    var foundSoFar = obj[properties[0]];
    var remainingProperties = properties.slice(1);

    return deepGet(foundSoFar, remainingProperties);
}

//If not found or value is null or undefined returns specified default value
function deepGet (obj, props, defaultValue) {
    // If we have reached an undefined/null property
    // then stop executing and return the default value.
    // If no default was provided it will be undefined.
    if (obj === undefined || obj === null) {
        return defaultValue;
    }

    // If the path array has no more elements, we've reached
    // the intended property and return its value
    if (props.length === 0) {
        return obj;
    }

    // Prepare our found property and path array for recursion
    var foundSoFar = obj[props[0]];
    var remainingProps = props.slice(1);

    return deepGet(foundSoFar, remainingProps, defaultValue);
}

var rels = {
    Viola: {
        Orsino: {
            Olivia: {
                Cesario: null
            }
        }
    }
};


sallyRel = deepGet(rels, ["Viola", "Harry", "Sally"], {});