我有一个javascript函数，我无法分辨自己做错了什么

Question

This is a program to ping several hosts and track their

Here is the offending function

function parseHistory(){
for(i = 0; i < hosts.length; i++){
    var countTotal = 0;
    var countSuccessful = 0;
    var timeTotal = 0;
    for(j = 0; j < history[hosts[i]].length; j++){
        if(history[hosts[i]][j].success){
            countTotal++;
            countSuccessful++;
            timeTotal += history[hosts[i]][j].time;
        } else {
            countTotal++;
        }
    }
    var uptimePercent = Math.round(countSuccessful / countTotal * 10000) / 100 + '%';
    var averageTime = Math.round(timeTotal / countSuccessful * 100) / 100;
    console.log('--- ' + hosts[i] + ' has ' + uptimePercent + ' uptime with an average round-trip time of ' + averageTime + 'ms');
}
console.log('---');
}

Where hosts is an array of strings, and history is an object that stores several arrays of result objects.

My main problem is with this for loop, it seems to be doing the math wrong but I can't tell where.

Here is the output my program produces after about 30 seconds

--- google.com has 100% uptime with an average round-trip time of 33ms
--- yahoo.com has 100% uptime with an average round-trip time of 112ms
--- <redacted> has 0% uptime with an average round-trip time of NaNms
--- 127.0.0.1 has 100% uptime with an average round-trip time of 2ms
---
--- google.com has 100% uptime with an average round-trip time of 11.67ms
--- yahoo.com has 100% uptime with an average round-trip time of 38ms
--- <redacted> has 66.67% uptime with an average round-trip time of 1ms
--- 127.0.0.1 has 100% uptime with an average round-trip time of 1.33ms
---
--- google.com has 100% uptime with an average round-trip time of 7.6ms
--- yahoo.com has 100% uptime with an average round-trip time of 23.4ms
--- <redacted> has 80% uptime with an average round-trip time of 0.75ms
--- 127.0.0.1 has 100% uptime with an average round-trip time of 1.2ms

The average times seem to be decreasing after every ping, but for no reason. It looks like a math error somewhere to me but I can't find it.

Can you tell me where my error is?

Full source: http://pastebin.com/G0mfBTPe

Answer 1

From your pastebin, I noticed that you continuously are lengthening the history[host] list:

setInterval(ping, pingIntervalMs, host, function(result){
    history[host].push(result);
    historyChanged = true;
});

What does the "result" structure look like? Perhaps you are pushing objects that default to ".success" but have zero ".time".