create-screenshots.js

var page = require('webpage').create();
var system = require('system');

var setExpected = system.args[2] == '-set-expected';
var imagesFolder = setExpected ? 'expected' : 'new';

var urlsAndBreakpoints = system.args[1];
var urls = urlsAndBreakpoints.split('-')[0].split(',');
var viewports = urlsAndBreakpoints.split('-')[1].split(',');
var viewportsObjects = [];

for (var i = 0; i < viewports.length; i += 2) {
    viewportsObjects.push({
        width: viewports[i],
        height: viewports[i + 1]
    })
}

var handlePage = function(url) {
    page.open(url, function() {
        var filename = url.replace(/https?:\/\//, '').replace(/\//g, '-');

        viewportsObjects.forEach(function(viewport, i) {
            page.viewportSize = { width: viewport.width, height: viewport.height };
            page.render('test/' + imagesFolder + '/' + filename + i + '.png');
        });

        nextPage();
    });
}

var nextPage = function() {
    var url = urls.shift();

    if (!url) {
        phantom.exit();
    }

    handlePage(url);
}

nextPage();