Function getTimingDataSync

src/service/variable-source.js:120–138

(win, startEvent, endEvent)

 *    if it is not yet available, or value as string
 */
export function getTimingDataSync(win, startEvent, endEvent) {
  const timingInfo = win['performance'] && win['performance']['timing'];
  if (!timingInfo || timingInfo['navigationStart'] == 0) {
    // Navigation timing API is not supported.
    return;
  }

  const metric =
    endEvent === undefined
      ? timingInfo[startEvent]
      : timingInfo[endEvent] - timingInfo[startEvent];

  if (!isFiniteNumber(metric) || metric < 0) {
    // The metric is not supported.
    return;
  } else {
    return metric;
  }
}

/**
 * Returns navigation information from the current browsing context.