add httpPost, update examples for http snippets

snippets/httpGet.md

@@ -2,7 +2,7 @@
 
 Makes a `GET` request to the passed URL.
 
-Use `XMLHttpRequest` web api to retrieve data from the given `url`. 
+Use `XMLHttpRequest` web api to make a `get` request to the given `url`.
 Handle the `onload` event, by running the provided `callback` function.
 Handle the `onerror` event, by running the provided `err` function.
 Omit the third argument, `err` to log the request to the console's error stream by default.
@@ -18,7 +18,7 @@ const httpGet = (url, callback, err = console.error) => {
 ```
 
 ```js
-httpGet('https://jsonplaceholder.typicode.com/posts', request => {
+httpGet('https://website.com/posts', request => {
   console.log(request.responseText);
-}) // 'Array of 100 items'
+}); // 'Retrieves all users from the database'
 ```

snippets/httpPost.md

@@ -0,0 +1,31 @@
+### httpPost
+
+Makes a `POST` request to the passed URL.
+
+Use `XMLHttpRequest` web api to make a `post` request to the given `url`.
+Set the value of an `HTTP` request header with `setRequestHeader` method.
+Handle the `onload` event, by running the provided `callback` function.
+Handle the `onerror` event, by running the provided `err` function.
+Omit the last argument, `err` to log the request to the console's error stream by default.
+
+```js
+const httpPost = (url, data, callback, err = console.error) => {
+    const request = new XMLHttpRequest();
+    request.open("POST", url, true);
+    request.setRequestHeader('Content-type','application/json; charset=utf-8');
+    request.onload = () => callback(request);
+    request.onerror = () => err(request);
+    request.send(data);
+}
+```
+
+```js
+const user = {
+    name: "Foo",
+    password: "fooBar"
+};
+const data = JSON.stringify(user);
+httpPost('https://website.com/posts', data, request => {
+  console.log(request.responseText);
+}); // 'Makes a new instance of user in database'
+```