utils.js

// give me some JSON based on the "?" params
function getJsonFromUrl() {
  var query = location.search.substr(1);
  if (query === "")
    return "";

  var data = query.split("&");
  var result = {};
  for (var i=0; i<data.length; i++) {
    var item = data[i].split("=");
    result[item[0]] = item[1];
  }
  return result;
}

// append to the "?" params to construct a new URL
function setUrlFromString(value) {
  var currentUrlJson = getJsonFromUrl();
  if (currentUrlJson == "") {
    return "?" + value;
  }

  var data = value.split("=");
  var result = []
  currentUrlJson[data[0]] = data[1];

  for (var key in currentUrlJson) {
    if (currentUrlJson.hasOwnProperty(key)) {
      result.push(key + "=" + currentUrlJson[key]);
    }
  }

  return "?" + result.join("&");
}

function parseLayerParam(number, options) {
  var defaultLayer = options.firstLayer ? 202 : 3;
  var canvas = document.querySelector("canvas");
  var num = Number(number);
  if (isNaN(num))
    num = defaultLayer;
  else if (num < 0 || num > 326)
    num = defaultLayer;

  options.firstLayer ? (canvas.dataset.layerOne = num) : (canvas.dataset.layerTwo = num);
  return num;
}

function parseFrameskipParam(number) {
  var canvas = document.querySelector("canvas");
  var num = Number(number);
  if (isNaN(num))
    return num = 1;
  else if (num < 1 || num > 10)
    return num = 1;

  canvas.dataset.frameskip = num;
  return num;
}

function parseAspectRatioParam(number) {
  var canvas = document.querySelector("canvas");
  var num = Number(number);
  if (isNaN(num))
    return num = 0;
  else if (num != 0 && num != 16 && num != 48 && num != 64)
    return num = 0;

  canvas.dataset.aspectRatio = num;
  return num;
}

function parseFullscreen(fullscreen) {
  if (fullscreen == "true") {
    setupFullscreen();
  }
}

function isIOS() {
  return /(iPad|iPhone|iPod)/gi.test(navigator.userAgent);
}

function isSafari() {
  return /\(KHTML, like Gecko\)\s+Version\//gi.test(navigator.userAgent);
}