example of a function to take a screenshot from within a Protractor 5 ( / Selenium 3) test case

screenshot_example.js

    function takeScreenShot(optionalFileNameFragment) {

      return browser.takeScreenshot().then(function (pngData) {
        var fragment = '' + (optionalFileNameFragment || "screenshot");
        var now      = new Date();
        var fullName = fragment + "-" + now.toISOString() + ".png";
        var fullPath = (process.env.CIRCLE_ARTIFACTS || "/tmp") + "/" + fullName;
        var stream   = fs.createWriteStream(fullPath);
        stream.write(new Buffer(pngData, 'base64'));
        stream.end();
        console.log("wrote screenshot: " + fullPath)
      });
    }