phantomjs page.evaluate not logging onto console

问题:

I am a PhantomJs newbie. Just checked a similar post on this site. My question is why 'foo' is not logged to console or printed?

var page = require('webpage').create()
var foo = 42;

function evaluate(page, func) {
    var args = [].slice.call(arguments, 2);
    var fn = "function() { return (" + func.toString() + ").apply(this, " + JSON.stringify(args) + ");}";
    return page.evaluate(fn);
}

page.open('http://google.com', function() {
  var foo = 42;
  evaluate(page, function(foo) {
  console.log(foo);
        },foo);

});

回答1:

The call page.evaluate() runs your evaluated code in a sandbox. The sandbox's console is not the same as PhantomJS's console.

The following lines added to your script will print your page's console to stderr.

var system = require('system');

page.onConsoleMessage = function(msg) {
    system.stderr.writeLine('console: ' + msg);
};

A more complete implementation would be:

var page = require('webpage').create()
var system = require('system');
var foo = 42;

page.onConsoleMessage = function(msg) {
  system.stderr.writeLine( 'console: ' + msg );
};

function evaluate(page, func) {
  var args = [].slice.call(arguments, 2);
  var fn = "function() { return (" + func.toString() + ").apply(this, " +     JSON.stringify(args) + ");}";
  return page.evaluate(fn);
}

page.open(
  'http://google.com',
  function() {
    var foo = 42;
    evaluate(
      page,
      function(foo) {
        console.log(foo);
      },
      foo
    );

    console.log( "Done" );

    phantom.exit( 0 ); // must exit somewhere in the script
  }
);

Outputs:

$ phantomjs /tmp/idiot.js 
console: 42
Done

By the way, you can call page.open using "about:blank" as your URL if you just want to sandbox test the evaluate function.

回答2:

Output to standard error did not work for me

a work around is assigning :

window.console.log = function(msg) { alert(msg) }; 

inside the page.evaluate

Then use :

page.onAlert = function(msg) {
  console.log(msg);
};

to catch the alert

回答3:

There were some problems in the past with console logging, but with the current version on phantomjs (1.9.8), you can do:

page.onConsoleMessage = function (msg) {
  console.log(msg);
};

then fire away your console.logs in the evaluate's callback:

page.evaluate(function() {
  console.log("some logged message");
});

回答4:

I'm using phantomjs to automate some Google Closure tests and ran into an issue I needed to debug. I was able to dispatch custom events from my test page and receive them inside page.evaluate.

File to log messages:

function logger(msg) {
  var evt = document.createEvent('CustomEvent');  // MUST be 'CustomEvent'
  evt.initCustomEvent('logger', false, false, msg);
  document.dispatchEvent(evt);
}

logger('my debug message');

Phantomjs file. Here I'm using a saveMessage method to store the string, but you can make that something more appropriate to your needs.

var exec = page.evaluate(function () {
  window.phantomRunner = new window.goog.testing.TestRunner();
  window.phantomTest = new window.goog.testing.TestCase();

  // Listen for `logger` events. The message is stored inside the event's detail property.
  document.addEventListener('logger', function(e) {
    window.phantomTest.saveMessage(e.detail);
  });

  window.phantomTest.autoDiscoverTests();
  window.phantomRunner.initialize(window.phantomTest);
  window.phantomRunner.execute();
  return (window.phantomTest.result_.messages);
})

回答5:

Make sure your phantomjs setting does not disable executing javascript

page.settings.javascriptEnabled = true;