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<!DOCTYPE html>
<style>
#detector { width: 5px; }
@media (-webkit-device-pixel-ratio:1) { #detector { width: 10px; } }
@media (-webkit-device-pixel-ratio:3) { #detector { width: 30px; } }
@media (-webkit-device-pixel-ratio:4) { #detector { width: 40px; } }
</style>
<script>
function devicePixelRatioFromStyle() {
var width = getComputedStyle(document.getElementById("detector")).width;
switch (width) {
case "10px":
return 1;
case "30px":
return 3;
case "40px":
return 4;
default:
return "unknown width: " + width;
}
}
</script>
<div id="detector"></div>
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