CasperJS没有'找不到jQuery

我正在使用jQuery选择器进行casper.js抓取。我知道有必要将jQuery调用放在casper.evaluate()中。

问题是在以下三个函数的最后中，提出了一个ReferenceError: Can't find variable: $。前两个非常好。

// On main page, scrape links to sub-pages.
function getLinks() {
    var links = $('li.ds-artifact-item a');
    return Array.prototype.map.call(links, function(e) {
        return e.getAttribute('href');
    });
}
// On main page, scrape sub-pages' titles.
function getTitles() {
    var titles = $('li.ds-artifact-item a');
    return Array.prototype.map.call(titles, function(e) {
        return e.innerHTML;
    });
}
// On sub-page, scrape document description.
function getDescription(){
    var descriptions = $('td.label-cell:contains(date)');
    return Array.prototype.map.call(descriptions, function(e) {
        return e.innerHTML;
    });
}

这是剧本的其余部分，不重要的细节被掩盖了。注意，anotherValidPage是返回HTTP 200（成功）的有效URL。

var links = []; var titles = []; var descriptions = [];
casper.start(validPage, function() {
    links = this.evaluate(getLinks);
    titles = this.evaluate(getTitles);
});

casper.then(function() {
    // echo results
    this.echo(links.length + ' links found:');
    this.echo(' - ' + links.join(''n - '));
    this.echo(titles.length + ' titles found:');
    this.echo(' - ' + titles.join(''n - '));
    });
casper.thenOpen(anotherValidPage, function(){});
casper.then(function(){
    // This call is the problematic one.
    descriptions = this.evaluate(getDescription());
    this.echo(descriptions.length + ' descriptions found:');
    this.echo(' - ' + descriptions.join(''n - '));
});
casper.run();