How to make a post with Widget?

Im trying using this function

function post_to_url(path, params, method) {
method = method || "post"; // Set method to post by default, if not specified.

// The rest of this code assumes you are not using a library.
// It can be made less wordy if you use one.
var form = document.createElement("form");
form.setAttribute("method", method);
form.setAttribute("action", path);

for(var key in params) {
if(params.hasOwnProperty(key)) {
var hiddenField = document.createElement("input");
hiddenField.setAttribute("type", "hidden");
hiddenField.setAttribute("name", key);
hiddenField.setAttribute("value", params[key]);

form.appendChild(hiddenField);
}
}

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

but doesnt work, it says that is a incorrect request and in firebug works ok.
The params are the way {key:value, ..., keyN:valueN}

How i can make a post?