isConnectionWorseThan3G.js

function isConnectionWorseThan3G() {
    // https://w3c.github.io/netinfo/#dfn-table-of-maximum-downlink-speeds
    var mbitsThreshold = 2;
    var connection = navigator.connection ||
                     navigator.mozConnection ||
                     navigator.webkitConnection;

    if (!connection) {
        return false;
    }

    // https://w3c.github.io/netinfo/
    if ('downlinkMax' in connection) {
        return connection.downlinkMax < mbitsThreshold;
    }

    // http://www.w3.org/TR/2012/WD-netinfo-api-20121129/
    if ('bandwidth' in connection) {
        return connection.bandwidth * 8 < mbitsThreshold;
    }

    // http://davidbcalhoun.com/2010/using-navigator-connection-android/
    if ('type' in connection) {
        return connection.type === connection.CELL_2G;
    }

    // default
    return false;
}