jquery.post.js

    // See https://stackoverflow.com/questions/133925/javascript-post-request-like-a-form-submit, jQuery version with arrays and objects support
    function post(path, parameters) {
        var form = $('<form></form>');

        form.attr("method", "post");
        form.attr("action", path);

        $.each(parameters, function(key, value) {
            if ( typeof value == 'object' || typeof value == 'array' ){
                $.each(value, function(subkey, subvalue) {
                    var field = $('<input />');
                    field.attr("type", "hidden");
                    field.attr("name", key+'[]');
                    field.attr("value", subvalue);
                    form.append(field);
                });
            } else {
                var field = $('<input />');
                field.attr("type", "hidden");
                field.attr("name", key);
                field.attr("value", value);
                form.append(field);
            }
        });
        $(document.body).append(form);
        form.submit();
    }

post('/contact/', {name: 'Johnny Bravo'});

Vanilla implementation :

function post(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();
}