get({ foo: { bar: 'bar' }}, 'foo.bar');

gistfile1.js

//
// https://jsfiddle.net/jmvf41f4/1/
//

function get(object, path) {
    var paths = path.split('.');
    var len = paths.length;
    var out = object;
    var i = 0;

    for (;i<len;i++) {
        out = out[paths[i]];
        if (!out && i < (len - 1)) { return; }
    }

    return out;
}

function set(object, path, value) {
    var paths = path.split('.');
    var len = paths.length;
    var cur = object;
    var i = 0;

    for (;i<len;i++) {
        if (i < (len - 1)) {
            if (cur[paths[i]] === undefined) {
                cur[paths[i]] = Object.create(null);
            }
        } else {
            cur[paths[i]] = value;
        }
 
        cur = cur[paths[i]];
    }
}

var a = {};

set(a, 'b.c.d.e.f.g', 'hello world');

console.log(get(a, 'b.c.d.e.f.g') === 'hello world');
console.log(get(a, 'b.c'));