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dmoath/jsbin.uRAZuxoJ.html

Last active January 4, 2016 15:39
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jsbin.uRAZuxoJ.html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta id="iView" name="viewport" content="width=device-width, initial-scale=1, maximum-scale=5, user-scalable=1" />
<title>Latency</title>
</head>
<body>
</body>
</html>
Raw
jsbin.uRAZuxoJ.js
var arrTimes = [];
var i = 0; // start
var tTimesToTest = 5;
var tThreshold = 117; //ms
var tAverage;
var testImage = "http://www.google.com/images/phd/px.gif";
var dummyImage = new Image();
/** test and average time took to download images from server, called recursively tTimesToTest times */
function testLatency(cb) {
var tStart = new Date().getTime();
if (i<tTimesToTest-1) {
dummyImage.src = testImage + '?t=' + tStart;
dummyImage.onload = function() {
//display error
var tEnd = new Date().getTime();
var tTimeTook = tEnd-tStart;
testLatency(cb);
arrTimes[i] = tTimeTook;
i++;
};
} else {
/** calculate average of array items then callback */
var sum = arrTimes.reduce(function(a, b) { return a + b; });
tAverage = sum / arrTimes.length;
cb(tAverage);
}
}
/** callback executes once everything is done */
var isConnectedFast = false;
testLatency(function(avg){
isConnectedFast = (avg <= tThreshold);
document.body.appendChild(
document.createTextNode("Time: " + (avg.toFixed(2)) + "ms - isConnectedFast? " + isConnectedFast)
);
});
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