casper.waitForSelector、超时和错误处理

Question

我制作了一个快速脚本来从 Reddit 帖子列表中截取屏幕截图。该脚本从 json 文件中获取 reddit 网址（示例如下所示），然后访问每个页面以捕获屏幕截图。

该脚本适用于大多数情况。但是，如果不满足 casper.waitForSelector 条件，它会偶尔 hang/continue 到运行。最终它会拖延整个服务器。我以为我做了足够的错误处理。我如何修改脚本以忽略任何不符合 casper.waitForSelector 条件的页面并继续进行下一个屏幕捕获项目？

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

如果您向 waitForSelector（第 3 个参数）提供 onTimeout 回调函数，那么它会在出错时执行而不是默认行为（停止脚本）。

您可以传入空函数或带有一些日志记录的函数：

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

如果您希望每个函数都有这种行为，您也可以将选项 casper.options.silentErrors 更改为 true。

casper.waitForSelector、超时和错误处理

casper.waitForSelector, timeout and error handling

javascript

casperjs