javascript - Casper JS 运行方法提前触发

Question

向函数添加 this.echo 命令会导致在设置链接之前调用 casper.run 方法

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

function getLinks() {
  this.echo("Getting links"); // <--------- This line cause everything to fail
  var links = document.querySelectorAll('table');
  return Array.prototype.map.call(links, function(e) {
    return e.getAttribute('id');
  });
}

var links = [];

casper.start('example.html', function() {
  links = this.evaluate(getLinks);
});

casper.run(function() {
  this.echo(links.length + ' links found:');
  this.echo(' - ' + links.join('\n - ')).exit();
});

Answer 1

从未使用过 casper.js，但来自 documentation :

As a reminder, think of the evaluate() method as a gate between the CasperJS environment and the one of the page you have opened; everytime you pass a closure to evaluate(), you’re entering the page and execute code as if you were using the browser console.

因此，this 可能不是指 casper，而是指文档的全局对象。 this.echo 不存在并抛出错误，函数的其余部分不会执行，也不会收集任何链接。所以，并不是传递给 run 的回调函数提前执行了，只是收集链接的代码从未运行过。

尝试使用 casper.echo("Getting links");，或者简单地删除调用并将其移动到 start 中:

casper.start('example.html', function() {
  this.echo("Getting links");
  links = this.evaluate(getLinks);
});