// Load the dynamic json file for highways, etc.
// Ref: https://codepen.io/KryptoniteDove/post/load-json-file-locally-using-pure-javascript
// Can also load .csv files
function loadJSON(inFile, callback)
{
    var xobj = new XMLHttpRequest();
    // Assume XML unless filename ends with .json
    if (inFile.endsWith(".json"))
    {
        xobj.overrideMimeType("application/json");
    }
    if (inFile.endsWith(".csv"))
    {
        xobj.overrideMimeType("text/csv");
    }
    xobj.open('GET', inFile, true);
    xobj.onreadystatechange = function()
    {
        if (xobj.readyState == 4 && xobj.status == "200")
        {
            callback(xobj.responseText);
        }
    };
    // We want ajax to ignore any cached responses
    xobj.setRequestHeader('If-Modified-Since', 'Sat, 01 Jan 2000 01:01:01 GMT')
    xobj.send(null);
}

/* Retrieve URL parameters passed to a web page
   @return a dictionary of key/value pairs
*/
function getQueryParms()
{
    var items = {};
    var query = window.location.search.substring(1);
    var parms = query.split("&");
    // Examine each parameter
    for (var i = 0, max = parms.length; i < max; i++)
    {
        // check for trailing & with no param
        if (parms[i] === "") 
            continue; // skip it

        var param = parms[i].split("=");
        // If it's valid add it to dictionary
        items[decodeURIComponent(param[0])] = decodeURIComponent(param[1] || "");
    }
    return items
}