asprin asprin - 3 months ago 51
Javascript Question

Using Multiple page.open in Single Script

My goal is to execute PhantomJS by using:

// adding $op and $er for debugging purposes
exec('phantomjs script.js', $op, $er);
print_r($op);
echo $er;


And then inside
script.js
, I plan to use multiple
page.open()
to capture screenshots of different pages such as:

var url = 'some dynamic url goes here';
page = require('webpage').create();
page.open(url, function (status) {
console.log('opening page 1');
page.render('./slide1.png');
});

page = require('webpage').create();
page.open(url, function (status) {
console.log('opening page 2');
page.render('./slide2.png');
});

page = require('webpage').create();
page.open(url, function (status) {
console.log('opening page 3');
page.render('./slide3.png');
phantom.exit(); //<-- Exiting phantomJS only after opening all 3 pages
});


On running
exec
, I get the following output on page:

Array ( [0] => opening page 3 ) 0


As a result I only get the screenshot of the 3rd page. I'm not sure why PhantomJS is skipping the first and second blocks of code (evident from the missing
console.log()
messages that were supposed to be output from 1st and 2nd block) and only executing the third block of code.

Answer

The problem is that the second page.open is being invoked before the first one finishes, which can cause multiple problems. You want logic roughly like the following (assuming the filenames are given as command line arguments):

function handle_page(file){
    page.open(file,function(){
        ...
        page.evaluate(function(){
            ...do stuff...
        });
        page.render(...);
        setTimeout(next_page,100);
    });
}
function next_page(){
    var file=args.shift();
    if(!file){phantom.exit(0);}
    handle_page(file);
}
next_page();

Right, it's recursive. This ensures that the processing of the function passed to page.open finishes, with a little 100ms grace period, before you go to the next file.

By the way, you don't need to keep repeating

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