ajax.js

// Simple ajax thing to send stuff
// @param url string
// @param success callback
// @param method string (optional)
// @param data plainobject (optional)
function ajax(url, success, method, data) {
    var xhr = new XMLHttpRequest();
    // Set the callback to use when all the stuff is done
    xhr.onreadystatechange = function() {
        // We are not interested in the 3 other stages
        if (xhr.readyState == XMLHttpRequest.DONE) {
            success(xhr.responseText)
        }
    }
    // Open using the provided method or 'get' if none
    xhr.open(method || 'get', url, true);
    if(method == 'post') {
        // Set the content-type in case of post
        xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    }

    if(data) {
        // Build data string if something is provided
        var res = [];
        for(var k in data) {
            res.push(encodeURIComponent(k) + '=' + encodeURIComponent(data[k]));
        }
        data = res.join('&');
    }
    // Send the request to the server using the provided data
    xhr.send(data);
}

// Examples
ajax('test.json', function(data) {
    console.log(JSON.parse(data));
});

ajax('index.html', function(data) {
    console.log(data);
});

ajax(window.location.href, function(data) {
    console.log(data);
}, 'post', { 'test' : 'yoh' });