YAHOO.util.Connect.setForm

http://developer.yahoo.com/yui/docs/YAHOO.util.Connect.html#method_setForm

 setForm
static string setForm ( form , optional )
This method assembles the form label and value pairs and constructs an encoded string. asyncRequest() will automatically initialize the transaction with a a HTTP header Content-Type of application/x-www-form-urlencoded.

Parameters:
    form  id or name attribute, or form object. 
    optional  enable file upload. 
    optional  enable file upload over SSL in IE only. 

Returns: string
    string of the HTML form field name and value pairs..

YUI ImageCropper 的簡單範例| 這樣做就對了

function onFormSubmit(e) { 
    YUE.preventDefault(e);
    YUC.setForm(form6);
    YUC.asyncRequest('POST', 'crop6.php', {
        success : function(o) {
            data = eval('(' + o.responseText + ')');
            img6.setAttribute('src', data.img);
            YUD.setStyle(img6, 'width', 'auto');
            YUD.setStyle(img6, 'height', 'auto');
            crop6.destroy();
            form6.parentNode.removeChild(form6);
        }
    });
}
YUE.on(form6, 'submit', onFormSubmit);