.evaluate doesn't provide current open page's document variable

[DWboutin]

Hi, i'm trying to get the document's scrollWidth and scrollHeight with evaluate, but it do nothing. I want to pass my pageWidth and pageHeight to the screenshot method. How can i do this?

var pageWidth;
var pageHeight;
var nightmare = new Nightmare();
var nightmare = new Nightmare();
var NRdashboard = nightmare
    .viewport(1920, 1080)
    .useragent('Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.93 Safari/537.36')
    .goto('https://login.newrelic.com/login')
    .wait()
    .type('#login_email', '***')
    .type('#login_password', '***')
    .click('#login_submit')
    .wait('body')
    .evaluate(function() {
        console.log('ASS');  // doesn't log
        console.log(document); // doesn't log
        pageWidth = document.body.scrollWidth;
        pageHeight = document.body.scrollHeight;
        return document.body.scrollWidth; // contains nothing
    })
    .screenshot(content_dir + '/dashboard.png')
    .goto('https://insights.newrelic.com/accounts/123456/dashboards/12345?kiosk=true')
    .wait(2000)
    .screenshot(content_dir + '/dashboard2.png')
    .run(function (err, nightmare) {
        if (err) return console.log(err);
        console.log('Done!');
        console.log(pageWidth, pageHeight); // undefined, undefined
    })
    .end();

[fmaruki-zz]

Variables inside the evaluate are in a different context than the functions from outside, so a variable won't be passed automatically. You need to pass variables from outside as the extra arguments of evaluate, and pass values back with return.

 var dimensions = yield nightmare.viewport(x, y) ... .evaluate(function() {
     ... ;
     return {pageWidth: pageWidth, pageHeight: pageHeight}
 }, arg1, arg2);
 var pageWidth = dimensions.pageWidth;

[DWboutin]

But how can i access do the document object of the page i'm currently in? I don't want to pass variables in, i want to get scrollHeight and scrollWidth of the page who are open.

I need to get document.body.scrollWidth, document.body.scrollHeight and change a variable in the localstorage.

Thank you for your quick response btw!

[DWboutin]

I tried to set things like you and the yield keyword. But it won't work. I have no arguments to pass to the evaluate methods.

function* newRelicDashboard(){

  var pageWidth;
  var pageHeight;

  var nightmare = Nightmare();

  yield nightmare
    .viewport(1920, 1080)
    .useragent('Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.93 Safari/537.36')
    .goto('https://login.newrelic.com/login')
    .wait()
    .type('#login_email', '***')
    .type('#login_password', '***')
    .click('#login_submit')
    .wait()
    .goto('https://insights.newrelic.com/accounts/123456/dashboards/12345?kiosk=true')
    .wait(2000);

  var pageWidth = yield nightmare
    .evaluate(function (selector) {
      // now we're executing inside the browser scope.
      return document.body.scrollWidth;
    });

  var pageHeight = yield nightmare
    .evaluate(function (selector) {
      // now we're executing inside the browser scope.
      console.log(document.body.scrollHeight); // nothing
      return document.body.scrollHeight;
    });

  yield nightmare
    .evaluate(function(){
      localStorage.setItem('kioskNoir', 'true');
    })
    .screenshot(content_dir + '/dashboard2.png')
    .run(function (err, nightmare) {
      if (err) return console.log(err);
      console.log('Done!');
      console.log(pageWidth, pageHeight);  // undefined, undefined
    })
    .end();
}

The .evaluate(function(){ localStorage.setItem('kioskNoir', 'true'); }) works some times, but not always.

[fmaruki-zz]

You need to wrap the generator function in a call with the libraries/functions vo or co, and start node with the flag --harmony (don't need flags for io.js).
Sorry for using yield, maybe it is not mandatory, I just never used nightmare without it.

[DWboutin]

All is working fine!

Why do you use vo exactly? I don't understand what it does.

Thank you for your help! Really appreciated

[fmaruki-zz]

I'm happy that you made it work!

Yield is like a return that can continue after the asynchronous operation is done. There must be someone wrapping the function to call it again as a callback once the result is set, so it can continue execution.

I usually use Co for this job, a library that I learned while programming with Koa.js. Vo looks like an sophisticated alternative to Co, I still don't know what it can do better for me.

Asynchronous callbacks, promisses, thunks and generators are all intimately related. It is a complex and fun topic, that I am still trying to fully understand.

Interesting links, I was trying to find another one, but can remember where it is:
https://www.promisejs.org/generators/
http://colintoh.com/blog/staying-sane-with-asynchronous-programming-promises-and-generators
https://medium.com/@rdsubhas/es6-from-callbacks-to-promises-to-generators-87f1c0cd8f2e

[DWboutin]

Thank you!

[rosshinkley]

It looks like this issue is resolved. Closing.