timeToFirstByte.js

/**
 * Takes a look at "time to first (last) byte" metrics
 */
"use strict";

module.exports = function (phantomas) {
  var measured = false;

  phantomas.setMetric("timeToFirstByte"); // @desc time it took to receive the first byte of the first response (that was not a redirect)
  phantomas.setMetric("timeToLastByte"); // @desc time it took to receive the last byte of the first response (that was not a redirect)

  phantomas.on("recv", function (entry, res) {
    // metrics already calculated
    if (measured) {
      return;
    }

    if (entry.isRedirect) {
      phantomas.log("Time to first byte: <%s> is a redirect", entry.url);
      return;
    }

    phantomas.setMetric("timeToFirstByte", entry.timeToFirstByte, true);
    phantomas.setMetric("timeToLastByte", entry.timeToLastByte, true);

    measured = true;

    phantomas.log(
      "Time to first byte: set to %d ms for request to <%s> (HTTP %d)",
      entry.timeToFirstByte,
      entry.url,
      entry.status,
    );
    phantomas.log("Time to last byte: set to %d ms", entry.timeToLastByte);

    phantomas.emit("responseEnd", entry, res); // @desc The first response (that was not a redirect) fully received
  });
};