使用casperjs时如何等待页面加载？

问题描述

我正在尝试抓取一个网页，其中包含许多下拉列表，并且表单中的值是相互依赖的。在许多方面，我需要代码等待页面刷新完成。例如，从列表中选择一个选项后，代码应该等到根据此选择填充下一个列表。如果有人可以指点，那将是非常有帮助的，因为奇怪的是我的代码只有在我提供了如此多的不必要的日志记录语句之后才能工作，这反过来又造成了一些延迟。任何改进代码的建议都会非常有用。

I am trying to scrape a webpage which has a form with many dropdowns and values in the form are interdependent. At many point I need the code to wait till the refresh of the page complete. Eg after selecting an option from the list, the code should wait till the next list is populated based on this selection. It would be really helpful if someone could give pointers because strangely my code is working only after I gave so much unnecessary logging statements which in-turn created some delay. Any suggestions to improve the code would be very helpful.

var casper = require('casper').create({
     verbose: true,
     logLevel: 'debug',
     userAgent: 'Mozilla/5.0  poi poi poi (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit/537.22 (KHTML, like Gecko) Chrome/25.0.1364.172 Safari/537.22',
     pageSettings: {}
 });

 casper.start('http://www.abc.com', function () {
     console.log("casper started");
     this.fill('form[action="http://www.abc.com/forum/member.php"]', {
         quick_username: "qwe",
         quick_password: "qwe"
     }, true);
     this.capture('screen.png');
 });
 casper.thenOpen("http://www.abc.com/search/index.php").then(function () {
     this.click('input[type="checkbox"][name="firstparam"]');
     this.click('a#poi');

     casper.evaluate(function () {
         document.getElementsByName("status")[0].value = 1;
         document.getElementsByName("state")[0].value = 1078;
         changeState(); //This function is associated with the dropdown ie state
and the page reloads at this point. Only after complete refresh the code shoud execute! How can this be achieved?
         return true;
     });
     this.echo('Inside the first thenOpen' + this.evaluate(function () {
         return document.search.action;
     }));
 });
 casper.then(function () {
     this.capture("poi.png");
     console.log('just before injecting jquery');
     casper.page.injectJs('./jquery.js');
     this.click('input[type="checkbox"][name="or"]');
     this.evaluate(function () {
         $('.boxline .filelist input:checkbox[value=18127]').attr("checked", true);
     });
     this.echo('Just before pressing the add college button' + this.evaluate(function () {
         return document.search.action;
     }));
     this.capture('collegeticked.png');
     if (this.exists('input[type="button"][name="niv"]')) {
         this.echo('button is there');
     } else {
         this.echo('button is not there');
     }
     this.echo("Going to print return value");
     this.click('input[type="button"][name="poi"]'); // This click again causes a page refresh. Code should wait at this point for completion.
     this.echo('Immediately after pressing the add college btn getPresentState()' + this.evaluate(function () {
         return getPresentState();
     }));
     this.echo('Immediately after pressing add colleg button' + this.evaluate(function () {
         return document.search.action;
     }));
     this.capture('iu.png');
 });

 casper.then(function () {
     console.log('just before form submit');
     this.click('form[name="search"] input[type="submit"]'); //Again page refresh. Wait.
     this.echo('Immediately after search btn getPresentState()' + this.evaluate(function () {
         return getPresentState();
     }));
     this.echo('Immediately after search button-action' + this.evaluate(function () {
         return document.search.action;
     }));
     this.capture("mnf.png");
 });

 casper.then(function () {
     casper.page.injectJs('./jquery.js');
     this.capture("resultspage.png");

     this.echo('Page title is: ' + this.evaluate(function () {
         return document.title;
     }), 'INFO');
     var a = casper.evaluate(function () {
           return $('tbody tr td.tdbottom:contains("tye") ').siblings().filter($('td>a').parent());
     });
     console.log("ARBABU before" + a.length);
 });

 casper.run();

推荐答案

我一直在使用提到的waitForSelector'解决方法'来自Arun：

I've been using the waitForSelector 'workaround' mentioned by Arun here:https://stackoverflow.com/a/22217657/1842033

这是我发现的最佳解决方案; '缺点'就是你需要知道你期望加载什么元素。我说缺点，我个人认为我没有遇到过这样的情况：我没有一些的反馈意见说我无论发生什么事都发生了

It's the best solution I've found; the 'drawback' as it were is that you need to be aware of what element you're expecting to load. I say drawback, personally I don't think I've encountered a situation where I've not had some kind of feedback saying that whatever I'm waiting for has happened

this.waitForSelector("{myElement}",
    function pass () {
        test.pass("Found {myElement}");
    },
    function fail () {
        test.fail("Did not load element {myElement}");
    },
    20000 // timeout limit in milliseconds
);

虽然我猜你可以使用或类似的东西，如果你没有视觉反馈。

Although I'd guess you could use waitForResource() or something like that if you didn't have visual feedback.

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