test the existence of property in a deep object structure

Question

In javascript, lets say I want to access a property deep in an object, for example:

entry.mediaGroup[0].contents[0].url

At any point along that structure, a

Answer 1

There are probably 3-4 different questions along this vein, and four times as many answers. None of them really satisfied me, so I made my own, and I'll share it.

This function is called "deepGet".

Example:

deepGet(mySampleData, "foo.bar[2].baz", null);

Here is the full code:

function deepGet (obj, path, defaultValue) {

    // Split the path into components
    var a = path.split('.');

    // If we have just one component left, note that for later.
    var last = (a.length) === 1;

    // See if the next item is an array with an index
    var myregexp = /([a-zA-Z]+)(\[(\d+)\])+/; // matches:  item[0]
    var match = myregexp.exec(a[0]);

    // Get the next item
    var next;
    if (match !== null) {
        next = obj[match[1]];
        if (next !== undefined) {
            next = next[match[3]];
        }
    } else {
        next = obj[a[0]];
    }

    if (next === undefined || next === null) {
        // If we don't have what we want, return the default value
        return defaultValue;
    } else {
        if (last) {
            // If it's the last item in the path, return it
            return next; 
        } else { 
            // If we have more items in the path to go, recurse
            return deepGet (next, a.slice(1).join("."), defaultValue); 
        }
    }
}

Here is a jsFiddle: http://jsfiddle.net/7quzmjh8/2/

I was inspired by these two things:

http://designpepper.com/blog/drips/making-deep-property-access-safe-in-javascript.html http://jsfiddle.net/wxrzM/1/

Hopefully this is useful to someone out there :)