Question

I need to post in the background with Greasemonkey. I tried to create an iframe dynamically and post to it, but it didn’t work:

function crossDomainPost() {
    // Add the iframe with a unique name
    var iframe = document.createElement("iframe");
    var uniqueString = "CHANGE_THIS_TO_SOME_UNIQUE_STRING";
    document.body.appendChild(iframe);
    iframe.style.display = "none";
    iframe.contentWindow.name = uniqueString;

    // construct a form with hidden inputs, targeting the iframe
    var form = document.createElement("form");
    form.target = uniqueString;
    form.action = "http://INSERT_YOUR_URL_HERE";
    form.method = "POST";

    // repeat for each parameter
    var input = document.createElement("input");
    input.type = "hidden";
    input.name = "INSERT_YOUR_PARAMETER_NAME_HERE";
    input.value = "INSERT_YOUR_PARAMETER_VALUE_HERE";
    form.appendChild(input);

    document.body.appendChild(form);
    form.submit();
}

Some people say even if we post, we won’t be able take the values. if we can’t, just making the user visit the page is enough. it can be in JS, jQuery, AJAX post. Not only the form-iframe trick.

Answer 1

Greasemonkey has built-in support for cross-domain posting. You do not need to use jsonp, nor an iframe. Use the GM_xmlhttpRequest function.

Rather than trying to build a form and post it, you send form-encoded data directly:

var formData1   = "1 INSERT_YOUR_PARAMETER_VALUE_HERE";
var formData2   = "2 INSERT_YOUR_PARAMETER_VALUE_HERE";
var formData3   = "3 INSERT_YOUR_PARAMETER_VALUE_HERE";
// etc.

GM_xmlhttpRequest ( {
    method:     "POST",
    url:        "http://YOUR_SERVER.COM/YOUR_PATH",
    data:       "formData1=" + encodeURIComponent (formData1)
                + "&" + "formData2=" + encodeURIComponent (formData2)
                + "&" + "formData3=" + encodeURIComponent (formData3)
                // etc.
                ,
    headers:    {
        "Content-Type": "application/x-www-form-urlencoded"
    },
    onload:     function (response) {
        console.log (response.responseText);
    }
} );