JS | GTM | window.performance.timing buckets

function(){
  var t = window.performance.timing, output = {};
  if(!t){
    output = {"pageLoadTime" : "NA", "connectTime" : "NA", "renderTime" : "NA"};
  }else{
    var  buckets = [0,250,500,750,1000,1250,1500,2000,2500,3000];
    var rawValues = {
      "pageLoadTime" : t.loadEventEnd - t.navigationStart,
      "connectTime" : t.responseEnd - t.requestStart,
      "renderTime" : t.domComplete - t.domLoading
    };
    for (var i = 0; i < buckets.length; i++){
      for (var key in rawValues) {
        var rvk = rawValues[key],
            low = buckets[i],
            suffix = { {var - Is beta}} ? " " + rvk : "";

      if ((i+1) == buckets.length && rvk > low){
        // last bucket = special case
        output[key] = low + "+" + suffix;
      }else{
        var high = buckets[i+1];
        if(rvk <= high && rvk >= low){
          output[key] = low + "-" + high + suffix;
        }
      }
    }
  }
}
return output;
}