如何在CasperJS中保存按钮点击触发的文件？

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

var url = 'http://example.com';

casper.start(url, function() {
    this.echo('Page loaded');
});

casper.then(function() {
    this.click('#saveButton');
});

casper.waitFor(function check() {
    return fs.exists('path/to/downloaded/file');
}, function then() {
    this.echo('File downloaded');
}, function timeout() {
    this.echo('Timeout').exit();
}, 10000); // 设置超时时间，单位为毫秒

casper.then(function() {
    var filePath = 'path/to/downloaded/file';
    var savePath = 'path/to/save/file';
    fs.copy(filePath, savePath);
});

casperjs saveFile.js