Google Script that returns zipcode for address.

getZip.js

function getZip(address) {
    if (address == '') {
        return 'ERROR: No address was provided';
    } else {
        var location = Maps.newGeocoder().geocoder.geocode(address);
        if (location.status == 'OK') return extractFromAddress(location.results[0].address_components, 'postal_code');
        else return 'ERROR: Something went wrong with Geocoder';
    }
}

function extractFromAddress(components, type) {
    for (var x = 0; x < components.length; x++) {
        for (var y = 0; y < components[x].types.length; y++) {
            if (components[x].types[y] == type) return components[x].long_name;
        }
    }
}