1//creating a button and linking it to bClicked()
2document.onload=()=>{
3  let b = documentbody.createElement("button");
4  b.onclick = bClicked;
5}
6
7function bClicked(){
8  //yourID is the id of element that you want to fullscreen 
9  document.getElementByID("yourID").requestFullscreen();
10}
11
12//to exit fullscreen
13document.exitFullscreen();

1$('#toggle_fullscreen').on('click', function(){
2  // if already full screen; exit
3  // else go fullscreen
4  if (
5    document.fullscreenElement ||
6    document.webkitFullscreenElement ||
7    document.mozFullScreenElement ||
8    document.msFullscreenElement
9  ) {
10    if (document.exitFullscreen) {
11      document.exitFullscreen();
12    } else if (document.mozCancelFullScreen) {
13      document.mozCancelFullScreen();
14    } else if (document.webkitExitFullscreen) {
15      document.webkitExitFullscreen();
16    } else if (document.msExitFullscreen) {
17      document.msExitFullscreen();
18    }
19  } else {
20    element = $('#container').get(0);
21    if (element.requestFullscreen) {
22      element.requestFullscreen();
23    } else if (element.mozRequestFullScreen) {
24      element.mozRequestFullScreen();
25    } else if (element.webkitRequestFullscreen) {
26      element.webkitRequestFullscreen(Element.ALLOW_KEYBOARD_INPUT);
27    } else if (element.msRequestFullscreen) {
28      element.msRequestFullscreen();
29    }
30  }
31});
32#container{
33  border:1px solid red;
34  border-radius: .5em;
35  padding:10px;
36}
37<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
38<div id="container">
39  <p>
40    <a href="#" id="toggle_fullscreen">Toggle Fullscreen</a>
41  </p>
42  I will be fullscreen, yay!
43</div>
44