feat: restructure docs into "chapters" (#12)

* feat(docker, k8s): create containers folder and kubernetes notes

docs/languages/javascript/ajax.md

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+# AJAX
+
+**AJAX**: Asynchronous JavaScript and XML
+
+AJAX Interaction:
+
+1. An event occurs in a web page (the page is loaded, a button is clicked)
+2. 2.An `XMLHttpRequest` object is created by JavaScript
+3. 3.The `XMLHttpRequest` object sends a request to a web server
+4. 4.The server processes the request
+5. 5.The server sends a response back to the web page
+6. 6.The response is read by JavaScript
+7. 7.Proper action (like page update) is performed by JavaScript
+
+## XMLHttpRequest
+
+```js
+var request = new XMLHttpRequest();
+
+request.addEventListener(event, function() {...});
+
+request.open("HttpMethod", "path/to/api", true);  // third parameter is asynchronicity (true = asynchronous)
+request.setRequestHeader(key, value)  // HTTP Request Headers
+request.send()
+```
+
+To check the status use `XMLHttpRequest.status` and `XMLHttpRequest.statusText`.
+
+### XMLHttpRequest Events
+
+**loadstart**: fires when the process of loading data has begun. This event always fires first
+**progress**: fires multiple times as data is being loaded, giving access to intermediate data
+**error**: fires when loading has failed
+**abort**: fires when data loading has been canceled by calling abort()
+**load**: fires only when all data has been successfully read
+**loadend**: fires when the object has finished transferring data always fires and will always fire after error, abort, or load
+**timeout**: fires when progression is terminated due to preset time expiring
+**readystatechange**: fires when the readyState attribute of a document has changed
+
+**Alternative `XMLHttpRequest` using `onLoad`**:
+
+```js
+var request = new XMLHttpRequest();
+request.open('GET', 'myservice/username?id=some-unique-id');
+request.onload = function(){
+    if(request.status ===200){
+        console.log("User's name is "+ request.responseText);
+    } else {
+        console.log('Request failed.  Returned status of '+ request.status);
+    }
+};
+request.send();
+```
+
+**Alternative `XMLHttpRequest` using `readyState`**:
+
+```js
+var request = new XMLHttpRequest(),  method ='GET',  url ='https://developer.mozilla.org/';
+
+request.open(method, url, true);
+request.onreadystatechange = function(){
+    if(request.readyState === XMLHttpRequest.DONE && request.status === 200){
+        console.log(request.responseText);
+    }
+};
+request.send();
+```
+
+`XMLHttpRequest.readyState` values:
+`0` `UNSENT`: Client has been created. `open()` not called yet.
+`1` `OPENED`: `open()` has been called.
+`2` `HEADERS_RECEIVED`: `send()` has been called, and headers and status are available.
+`3` `LOADING`: Downloading; `responseText` holds partial data.
+`4` `DONE`: The operation is complete.
+
+### `XMLHttpRequest` Browser compatibility
+
+Old versions of IE don't implement XMLHttpRequest. You must use the ActiveXObject if XMLHttpRequest is not available
+
+```js
+var request =window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject('Microsoft.XMLHTTP');
+
+// OR
+
+var request;
+if(window.XMLHttpRequest){
+    // code for modern browsers  
+    request = new XMLHttpRequest();
+} else {
+    // code for old IE browsers
+    request = new ActiveXObject('Microsoft.XMLHTTP');
+}
+```
+
+## Status & Error Handling
+
+Always inform the user when something is loading. Check the status and give feedback (a loader or message)
+Errors and responses need to be handled. There is no guarantee that HTTP requests will always succeed.
+
+### Cross Domain Policy
+
+Cross domain requests have restrictions.
+
+Examples of outcome for requests originating from: `http://store.company.com/dir/page.htmlCross-origin`
+
+| URL                                             | Outcome | Reason             |
+|-------------------------------------------------|---------|--------------------|
+| `http://store.company.com/dir2/other.html`      | success |
+| `http://store.company.com/dir/inner/other.html` | success |
+| `https://store.company.com/secure.html`         | failure | Different protocol |
+| `http://store.company.com:81/dir/other.html`    | failure | Different port     |
+| `http://news.company.com/dir/other.html`        | failure | Different host     |