如何在casperjs中循环 [英] How to for loop in casperjs

问题描述

我试图点击下一个按钮N次并每次抓取页面源。我知道我可以在远程网站上运行任意函数，所以我只使用远程函数nextPage（）而不是click（）我如何运行以下任意次数：

I am trying to click a 'next' button N number of times and grab the page source each time. I understand that I can run an arbitrary function on the remote website, so instead of click() I just use the remote function nextPage() How do I run the following, an arbitrary number of times:

var casper = require('casper').create();

casper.start('http://www.example.com', function() {

    this.echo(this.getHTML());
    this.echo('-------------------------');

    var numTimes = 4, count = 2;

    casper.repeat(numTimes, function() {
        this.thenEvaluate(function() {
            nextPage(++count);
        });

        this.then(function() {
            this.echo(this.getHTML());
            this.echo('-------------------------');
        });
    });

});

'我'这是我尝试在javascript中使用的索引for循环。

'i' here is an index I tried to use in a javascript for loop.

所以tl;博士：我想舔'下一步'，打印页面来源，点击'下一步'，打印页面来源，点击'下一步'...继续N次。

So tl;dr: I want lick 'next', print pages source, click 'next', print page source, click 'next'... continue that N number of times.

推荐答案

首先，您可以将值传递给远程页面上下文（即 thenEvaluate 这样的函数：

First, you can pass a value to the remote page context (i.e. to thenEvaluate function like this:

    this.thenEvaluate(function(remoteCount) {
        nextPage(remoteCount);
    }, ++count);

然而， Casper #repact 可能不是一个好用的函数，因为循环不会等待每个页面加载然后捕获内容。

However, Casper#repeat might not be a good function to use here as the loop would NOT wait for each page load and then capture the content.

你可能宁愿设计一个基于事件的链接。

You may rather devise a event based chaining.

代码的工作流程是：

1. 将一个全局变量（或者至少是下面提到的函数可访问的变量）存储到stor e 计数和限制。

收听 load.finished 事件并在此处抓取HTML，然后调用下一页。

listen to the load.finished event and grab the HTML here and then call the next page.

A简化代码可以是：

var casper = require('casper').create();

var limit = 5, count = 1;

casper.on('load.finished', function (status) {
    if (status !== 'success') {
        this.echo ("Failed to load page.");
    }
    else {
        this.echo(this.getHTML());
        this.echo('-------------------------');
    }



    if(++count > limit) {
        this.echo ("Finished!");

    }
    else {
        this.evaluate(function(remoteCount) {
            nextPage(remoteCount);
            // [Edit the line below was added later]
            console.log(remoteCount);
            return remoteCount;
        }, count);

    }

});

casper.start('http://www.example.com').run();

注意：如果您使用高负载的JS流程等页面，可能还想在调用nextPage之前添加 wait ：

this.wait( 
   1000, // in ms
   function () {
        this.evaluate(function(remoteCount) {
            nextPage(remoteCount);
        }, count);
   }
);     

以下事件监听器将帮助您进行调试。

The following event listeners will help you debug.

// help is tracing page's console.log 
casper.on('remote.message', function(msg) { 
    console.log('[Remote Page] ' + msg); 
}); 

// Print out all the error messages from the web page 
casper.on("page.error", function(msg, trace) { 
    casper.echo("[Remote Page Error] " + msg, "ERROR"); 
    casper.echo("[Remote Error trace] " + JSON.stringify(trace, undefined, 4)); 
});

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