PhantomJS working example

loadspeed.js

var page = require('webpage').create(),
    system = require('system'),
    t, address;

if (system.args.length === 1) {
    console.log('Usage: loadspeed.js <some URL>');
    phantom.exit();
}

t = Date.now();
address = system.args[1];
page.viewportSize = { width: 600, height: 600 };
page.open(address, function (status) {
    if (status !== 'success') {
        console.log('FAIL to load the address');
        phantom.exit();
    } else {
        t = Date.now() - t;
        window.setTimeout(function () {
            console.log('Loading time ' + t + ' msec');
            page.render('screenshot.png');
            phantom.exit();
        }, 200);
    }
});