Best practice looping through a JavaScript object [duplicate]

You can do a test like this:

function representsNumber(str) {
    return str === (+str).toString();
}

// E.g. usage
representsNumber('a'); // false
representsNumber([]); // false
representsNumber(1); // false (it IS a number)
representsNumber('1.5'); // true
representsNumber('-5.1'); // true
representsNumber('NaN'); // true

And recurse over all your nodes. Overkill example:

function seeker(o, test, _true, _false) {
    _true || (_true = function (e) {return e;});
    _false || (_false = function (e) {return e;});
    function recursor(o) {
        var k;
        if (o instanceof Array)
            for (k = 0; k < o.length; ++k) // Iterate over an array
                if (typeof o[k] !== 'object')
                    o[k] = test(o[k]) ? _true(o[k]) : _false(o[k]);
                else
                    recursor(o[k]);
        else
            for (k in o) // Iterate over an object
                if (typeof o[k] !== 'object')
                    o[k] = test(o[k]) ? _true(o[k]) : _false(o[k]);
                else
                    recursor(o[k]);
    }
    if (typeof o === "object") 
        return recursor(o), o;
    else 
        return test(o) ? _true(o) : _false(o); // Not an object, just transform
}

// Sample usage
seeker({foo: [{bar: "20"}]}, representsNumber, parseFloat);
// {foo: [{bar: 20}]}