如何让鬼马小精灵。js http。状态码?

I have simple code below:

我有简单的代码如下:

var casper = require("casper").create({
    }),
    utils = require('utils'),
    http = require('http'),
    fs = require('fs');

casper.start();

casper.thenOpen('https://www.yahoo.com/', function() {
    casper.capture('test.png');
});

casper.on('http.status.404', function(resource) {
  this.echo('wait, this url is 404: ' + resource.url);
});

casper.run(function() {
  casper.exit();
});
var ca