用javascript计算RTT问题

Question

我想测量RTT到服务器的时间...这就是问题所在，当我有以下工作时，它可以完美地工作：

var start = new Date();
var startTime=start.getMilliseconds();

document.write('<img src="http://mysite.com/myfile.gif" onload="getEndTime()">');


function getEndTime()
{
    var stop= new Date();
    var t=stop.getMilliseconds()-startTime;
    console.log(t);
 }

但是，如果我想将t存储在一个变量中，并将其从函数中打印出来，那么它在大多数情况下都不起作用！

例如：

var start = new Date();
var startTime=start.getMilliseconds();

document.write('<img src="http://mysite.com/myfile.gif" width="1" height="1" onload="getEndTime()">');

var rtt;

function getEndTime()
{
    var stop= new Date();
    var t=stop.getMilliseconds()-startTime;
    rtt=t;
}

console.log(rtt);

rtt大部分时间将为0！！...有人能帮上忙吗？这太令人沮丧了！

Answer 1

您从不调用getEndTime (我看得出来)，那么如何设置rtt (在调用console.log时)。

也许可以在页面上添加一个按钮，或者在分配了rtt之后添加console.log

我所看到的分页步骤：

1. Load up globals (start，startTime，define function等)
2. 声明您希望将代码输出到页面，并在load
3. Immediately转储时触发(未定义) variable
4. ...
5. OnLoad实际触发，但未输出任何内容。

var begin = new Date,
    rtt = [],
    imgs = [
        'http://myserver.com/foo.gif',
        'http://myserver.com/bar.gif'
        // etc.
    ];

function getEndTime(){
    var end = new Date;
    var delta = end.getMilliseconds() - begin.getMilliseconds();
    console.log('image loaded in ' + delta + 'ms');
    rtt.push(delta);
}
function dumpSummary(){
    // based on the number of entried in our rtt array, we can determine
    // if all the images have been loaded. if not, re-call this function (with
    // a delay until we reach it.
    if (rtt.length == imgs.length){
        console.log('All images have loaded. Their times are:');
        for (var r = 0; r < rtt.length; r++){
            console.log(r + '. ' + rtt[r]);
        }
    }else{
        console.log('waiting on more images...');
        // not enough entries, try again later
        setTimeout(dumpSummary,1000);
    }
}
// begin polling for the "finish line"
dumpSummary();

// output the images one-by-one
console.log('beginning');
for (var i = 0; i < imgs.length; i++)
    document.write('<img src="' + imgs[i] + '" width="1" height="1" alt="" onload="getEndTime();" />');