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Performance.now() polyfill
(function(w){
var perfNow;
var perfNowNames = ['now', 'webkitNow', 'msNow', 'mozNow'];
if(!!w['performance']) for(var i = 0; i < perfNowNames.length; ++i)
{
var n = perfNowNames[i];
if(!!w['performance'][n])
{
perfNow = function(){return w['performance'][n]()};
break;
}
}
if(!perfNow)
{
perfNow = Date.now;
}
w.perfNow = perfNow;
})(window);
// Usage
console.log(window.perfNow());
@meowgorithm

Note that Date.now() doesn't exist in IE8, so you may also need to add something along the lines of:

if(Date.now) {
    perfNow = Date.now();
} else {
    perfNow = +(new Date());
}
@dsamarin
dsamarin commented Jun 1, 2013
+(new Date()) // this is a number
function now() { return +(new Date()); } // this is a function that returns a number
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