nightwatch usefull commands

saveElementScreenshot.js

const assert = require('assert');
const Jimp = require('jimp');

exports.command = function (selector, fileName) {

  this.perform((client, done) => {

    let width, height, x, y;

    client
      .saveScreenshot(fileName)

      .getLocationInView(selector, position => {
        ({x, y} = position.value);
      })

      .getElementSize(selector, size => {
        ({width, height} = size.value)
      })

      .perform((client, done) => {
        Jimp
          .read(fileName, function (err, image) {
            image
              .crop(x, y, width, height)
              .write(fileName, () => {
                done();
              })
          })
      });
    done()
  });

  return this;
};