casper.waitForSelector，超时和错误处理

Question

我做了一个快速的脚本来捕获Reddit帖子列表的屏幕截图。脚本从json文件中获取reddit URL（如下所示），然后访问每个页面以捕获屏幕截图。

该脚本最适用。但是，如果不符合标准casper.waitForSelector，每隔一段时间它将挂起/继续运行。最终它会拖延整个服务器。我以为我正在做足够的错误处理。如何修改脚本以忽略任何不符合casper.waitForSelector条件的页面，然后转到下一个屏幕截图项目？

JS

var casper = require('casper').create({ 
    verbose: true, 
    viewportSize: { 
     width: 1280, 
     height: 720 
    }, 
    logLevel: 'error', 
    pageSettings: { 
     ignoreSslErrors: true, 
     loadImages: true, // load images 
     loadPlugins: true, // do not load NPAPI plugins (Flash, Silverlight, ...) 
     webSecurityEnabled: false, // ajax 
     userAgent: 'Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/29.0.1547.2 Safari/537.36' 
    } 
}); 

//Create random names for files 
function randString(x) { 
    var s = ""; 
    while (s.length < x && x > 0) { 
     var r = Math.random(); 
     s += (r < 0.1 ? Math.floor(r * 100) : String.fromCharCode(Math.floor(r * 26) + (r > 0.5 ? 97 : 65))); 
    } 
    return s; 
} 


function getReddit(reddit, filename) { 
    casper.thenOpen(reddit, function() { 
     if (casper.exists("#thing_" + filename)) { 
      casper.waitForSelector("#thing_" + filename, function() { 
       casper.captureSelector(randString(10) + '.png', "#thing_" + filename, { 
        quality: 100 
       }); 
      }); 
     } else { 
      console.log("Reddit Error: " + filename); 
     } 
    }); 
} 

var link = 'http://localhost/test.json'; 

casper.start(link); 

casper.on("resource.received", function(resource) { 
    var results = this.evaluate(function(url) { 
     return __utils__.sendAJAX(url, "GET"); 
    }, resource.url); 
    var x = JSON.parse(results); 
    //this.echo(x.length); 
    for (var i = 0; i < x.length; ++i) { 
     var reddit = x[i].post_url; 
     var filename = x[i].id; 
     getReddit(reddit, filename); 
    } 
}); 

casper.run(); 

JSON

{ 
post_url: "https://www.reddit.com/r/todayilearned/comments/4marhg/til_that_in_the_16th_century_christians_called/", 
bit_id: "l6KE0vzMmgQ", 
id: "t3_4marhg" 
}, 
{ 
post_url: "https://www.reddit.com/r/videos/comments/4mbbab/man_ignores_museum_rules_touches_priceless_clock/", 
bit_id: "2GK22rGYWKx", 
id: "t3_4mbbab" 
}, 
{ 
post_url: "https://www.reddit.com/r/space/comments/4mc1av/an_alien_world_67p_as_seen_by_rosetta_two_days_ago/", 
id: "t3_4mc1av" 
}, 
{ 
post_url: "https://www.reddit.com/r/worldnews/comments/4mc8uv/young_fish_become_hooked_on_eating_plastic_in_the/", 
id: "t3_4mc8uv" 
}, 
{ 
post_url: "https://www.reddit.com/r/todayilearned/comments/4mcda3/til_that_the_giant_tortoise_did_not_receive_a/", 
id: "t3_4mcda3" 
}, 
{ 
post_url: "https://www.reddit.com/r/science/comments/4mcl0y/a_new_study_has_shown_that_mothers_who_are/", 
id: "t3_4mcl0y" 
}, 
{ 
post_url: "https://www.reddit.com/r/news/comments/4mcveg/bp_agrees_to_pay_175_million_to_settle_claims_by/", 
id: "t3_4mcveg" 
}, 
{ 
post_url: "https://www.reddit.com/r/todayilearned/comments/4mdddw/til_that_when_a_british_captive_officer/", 
id: "t3_4mdddw" 
} 

Answer 1

如果您提供的onTimeout回调函数waitForSelector（第三个参数），那么它就会被执行，而不是默认的行为（停止脚本）出错。

您可以通过在一个空函数或一些日志记录功能：

casper.waitForSelector("#thing_" + filename, function _then() { 
    this.captureSelector(randString(10) + '.png', "#thing_" + filename, { 
     quality: 100 
    }); 
}, function _onTimeout(){ 
    this.echo("#thing_" + filename + " not found", "WARNING"); 
}); 

您还可以，如果你想这种行为对每个功能更改选项casper.options.silentErrors到true。