如何在外部Javascript中正确使用它

我有两个javascript函数工作良好，只要我保持他们在我的头标签的HTML，但我想把它们移动到一个外部的javascript文件。

function uploadImageSB() {
    Shadowbox.init({});
    // shadowbox for image upload
    Shadowbox.open({
        content: 'photo.cgi?function=photo_upload',
        player: 'iframe',
        title: 'Image Upload',
        height: 200,
        width: 500,
        options: {
            onFinish: function () {
                // get the iframe
                var iframe = document.getElementById('sb-player');
                var formName = 'photoForm';
                // add an event listener to determine when the sb form is fully loaded
                if (iframe.addEventListener) {
                    // use addEventListener for Safari, Chrome, Firefox
                    iframe.addEventListener("load", getTA(formName), true);
                } else {
                    // use attachEvent for IE
                    iframe.attachEvent("onload", getTA(formName));
                }
            }
        }
    })
};

上面的javascript调用下一个函数:

function getTA(fn) {
    // get the contents of the tinymce editor
    var ed = tinymce.activeEditor;
    var content = ed.save();
    // dynamically create textarea
    var ta = document.createElement('textarea');
    ta.textContent = content;
    ta.name = 'article';
    ta.value = ta.textContent;
    // get the iframe content
    var iframeContent = this.contentDocument || this.contentWindow.document;
    // append the textarea to the shadowbox form, but do not display it
    var form = iframeContent.getElementById(fn);
    form.appendChild(ta);
    form.getElementsByTagName('textarea')[0].style.display = 'none';
};

我认为问题是我在这里使用this:

var iframeContent = this.contentDocument || this.contentWindow.document;

但我不知道如何解决它。谢谢。