What is the best way to have js return undefined rather than throw an error when a parent property does not exist?

Example

a = {}
b = a.x.y.z
// Error: Cannot read property 'value' of undefined
// Target result: b = undefined

What is the best way to have js return undefined rather than throw an error when a parent property does not exist?

Example

a = {}
b = a.x.y.z
// Error: Cannot read property 'value' of undefined
// Target result: b = undefined

• javascript

• If you don't want to fill your code with a lot of try/catch (that is somehow a solution), in JS usually you check if an object is defined before using a specific property / method of it. It means, in that case, that you should verify that a has x, before access to it, and so on. If you using that approach to simulate namespaces, you can create your own function that do this operation recursively for you. – ZER0 Commented Jun 7, 2012 at 17:11

4 Answers 4

You have to check for the existence of each property:

var b;
if (a.x && a.x.y && a.x.y.z) {
    b = a.x.y.z
}

Or, simliar to another poster's "safeGet" function:

var get = function (obj, ns) {
    var y = ns.split('.');
    for(var i = 0; i < y.length; i += 1) {
        if (obj[y[i]]) {
            obj = obj[y[i]];
        } else {
            return;
        }
    }
    return obj;
};

Use:

var b = get(a, 'x.y.z');

try {
  a = {}
  b = a.x.y.z
}
catch (e) {
  b = void 0;
}

I would go for slightly verbose:

var b = ((a.x || {}).y || {}).z

you could write a safeGet helper function, something like:

edited for drilldown as suggested in ments by arcyqwerty

var getter = function (collection, key) {
    if (collection.hasOwnProperty(key)) {
        return collection[key];
    } else {
        return undefined;
    }
};

var drillDown = function (keys, currentIndex, collection) {
    var max = keys.length - 1;
    var key = keys[currentIndex];

    if (typeof collection === 'undefined') {
        return undefined;   
    }

    if (currentIndex === max) {
        return getter(collection, key);
    } else {
        return drillDown(keys, currentIndex + 1,
                         getter(collection, key));
    }
};

var safeGet = function (collection, key) {
    if (key.indexOf(".") !== -1) {
        return drillDown(key.split("."), 0, collection);
    } else {
        return getter(collection, key);
    }
};

a = { x: 1 };
b = safeGet(a, 'x.y.z');

http://jsfiddle/YqdWH/2/