一段简单的显示当前页面FPS的代码

 1 var showFPS = (function () {
 2     // noinspection JSUnresolvedVariable, SpellCheckingInspection
 3     var requestAnimationFrame =
 4         window.requestAnimationFrame || //Chromium  
 5         window.webkitRequestAnimationFrame || //Webkit 
 6         window.mozRequestAnimationFrame || //Mozilla Geko 
 7         window.oRequestAnimationFrame || //Opera Presto 
 8         window.msRequestAnimationFrame || //IE Trident? 
 9         function (callback) { //Fallback function 
10             window.setTimeout(callback, 1000 / 60);
11         };
12 
13     var dialog;
14     var container;
15 
16     var fps = 0;
17     var lastTime = Date.now();
18 
19     function setStyle(el, styles) {
20         for (var key in styles) {
21             el.style[key] = styles[key];
22         }
23     }
24 
25     function init() {
26         dialog = document.createElement(‘dialog‘);
27         setStyle(dialog, {
28             display: ‘block‘,
29             border: ‘none‘,
30             backgroundColor: ‘rgba(0, 0, 0, 0.6)‘,
31             margin: 0,
32             padding: ‘4px‘,
33             position: ‘fixed‘,
34             top: 0,
35             right: ‘auto,‘,
36             bottom: ‘auto‘,
37             left: 0,
38             color: ‘#fff‘,
39             fontSize: ‘12px‘,
40             textAlign: ‘center‘,
41             borderRadius: ‘0 0 4px 0‘
42         });
43         container.appendChild(dialog);
44     }
45 
46     function calcFPS() {
47         offset = Date.now() - lastTime;
48         fps += 1;
49 
50         if (offset >= 1000) {
51             lastTime += offset;
52             displayFPS(fps);
53             fps = 0;
54         }
55 
56         requestAnimationFrame(calcFPS);
57     };
58 
59     function displayFPS(fps) {
60         var fpsStr = fps + ‘ FPS‘;
61 
62         if (!dialog) {
63             init();
64         }
65 
66         if (fpsStr !== dialog.textContent) {
67             dialog.textContent = fpsStr;
68         }
69     }
70 
71     return function (parent) {
72         container = parent;
73         calcFPS();
74     };
75 })();
76 
77 showFPS(document.body);