JavaScript page rendering speed test script sharing_javascript skills

Copy code The code is as follows:

/* Get the timestamp of the start of rendering and save it in the array PAGE_SPEED_TIME* /

......

Copy code The code is as follows:

......
/* Page At the end, calculate the time it takes to load the page*/

Let’s analyze the contents of the page_speed_v2.js file. Reformat this script to make it easier to read.

Copy code The code is as follows:

/* 执行匿名函数构建对象PageSpeed */
;(function() {
    PageSpeed = {};/* 这里没有 var 关键字, 相当于引用的是 window.PageSpeed */

 /**
     * 绑定createScript方法
  *
  * @param String a script标签的src属性的值
  * @param String b script标签的id属性的值
  */
    PageSpeed.createScript = function(a, b) {
        var c = null;

        if (document.getElementById(b)) { /* script标签已经存在 */
            c = document.getElementById(b)
        } else { /* 不存在, 创建script标签 */
            c = document.createElement('script');
            var d = null;
            if (document.getElementsByTagName) {
                d = document.getElementsByTagName('head')[0] || document.documentElement;
            } else {
                d = document.documentElement;
            }
            d.insertBefore(c, d.firstChild); /* 调用insertBefore方法, 将新创建的script标签插入为第一个子元素 */
        }

  /* 这里的花括号起到代码片段分组功能 */
  {
            c.setAttribute('type', 'text/html');
            c.setAttribute('style', 'display:none;');
            c.setAttribute('charset', 'gb2312');
            c.setAttribute('id', b);
            c.setAttribute('src', a);
        }

        return c; /* 返回创建成功的script标签元素 */
    };

 /**
     * 绑定 submitDataForPageSpeed 方法
  *
  * @param Object a Map对象
  */
    PageSpeed.submitDataForPageSpeed = function(a) {
        var b = {
            'name': '',
            'rate': 0
        };
        b.name = a.name;
        b.rate = a.rate;

  /* a.PAGE_SPEED_TIME数组的最后一个元素减去第一个元素 */
        b['1'] = a.PAGE_SPEED_TIME[a.PAGE_SPEED_TIME.length - 1] - a.PAGE_SPEED_TIME[0];

        for (var i = 1; i < a.PAGE_SPEED_TIME.length - 1; i++) {
            b[(i + 1) + ''] = a.PAGE_SPEED_TIME[i] - a.PAGE_SPEED_TIME[0]
        }

  /* 提交速度测试结果的目的脚本 */
        var c = 'http://pagespeed-ied.qq.com/r.cgi';

  /* 遍历 b 数组的元素, 构建 query string */
        var d = [];
        for (var p in b) {
            d.push(p + '=' + b[p])
        }
        c += '?' + d.join('&');

  /* 创建script标签提交测速结果 */
        PageSpeed.createScript(c, 'submitForPageSpeed')
    };

 /**
  * 绑定 defaultSubmit 方法
  *
  */
    PageSpeed.defaultSubmit = function() {
        var a = '';
        try {
            a = location.host
        } catch(e) {}

var b = {
'name': a,
'rate': 1,
'PAGE_SPEED_TIME': []
};

if (!b.name) {
return
}

        if (! (typeof(PAGE_SPEED_TIME) == 'object' && PAGE_SPEED_TIME instanceof Array)) {
                                                                                                                                                           
/* Get new timestamp */

PAGE_SPEED_TIME.push(new Date().getTime());

b.PAGE_SPEED_TIME = PAGE_SPEED_TIME;

/*

* I don’t understand why a new variable aaa is needed here. Isn’t it possible to use a directly?

* The try ... catch structure uses a new variable aaaa but It has never been used later, why? Should it be aaa?
*/
var aaa = '';
try {
aaaa = location.host
} catch(e) {}

var c = Math.floor(Math.random() * 10000);

If (aaa == "ktv.qq.com" || aaa == "ttd.qq.com" || aaa == "tian.qq.com" || aaa == "sura.qq.com " || aaa == "gw.tnt.qq.com" || aaa == "007.qq.com") {

                    c = Math.floor(Math.random() * 1000);

}

/* Submit data with random probability */

If (c <= b.rate * 1) {

PageSpeed.submitDataForPageSpeed(b);
}
};

/**

* Bind submit method (used for CDN speed test?)

*
* @param String a Name
*/
PageSpeed.submit = function(a) {
var b = PageSpeed.cdn_page_speed_submitData;
var c = {};
for (var p in b) {
                c[p] =                                                                                     })();

try {
/* Try to submit data after 1 second*/
setTimeout(function() {
PageSpeed.defaultSubmit()
},
1000);

} catch(e) {}

/* The last comment, the second paragraph is a 32-digit hexadecimal number, which should be similar to ETag used to mark the content version */
/* |xGv00|ca82276cd78ac911d3d4310ba1408236 */