JSFiddle - React, Tailwind, and code Playground

HTML

<canvas id="timer" width="400" height="400" style="background: green; width:100%"></canvas>

JavaScript

var timer= document.getElementById('timer');
		var timerCTX= timer.getContext("2d");

		function displayTime(percent){
			var zero=-Math.PI/2;
			var full= Math.PI*2;
			
			// lets draw the background circle first.
			timerCTX.strokeStyle="#555";
			timerCTX.lineWidth = 6.5;
			timerCTX.beginPath();
			timerCTX.arc(timer.width/2, timer.width/2, (timer.width/2)-10, zero, full, false); 
			timerCTX.stroke();

			// now lets draw our percentage circle.
			timerCTX.strokeStyle="#bef";
			timerCTX.lineWidth = 8;
			timerCTX.beginPath();
			timerCTX.arc(timer.width/2, timer.width/2, (timer.width/2)-10,zero,(full*percent)+zero, false); 
			timerCTX.stroke();
		}
		
		var difference=0;
		var today = new Date();
		var startDate = new Date('Sept 3 2013 14:59:01 GMT-0400 (EDT)');
		var launchDate= new Date('Sept 3 2013 15:10:01 GMT-0400 (EDT)');

		setInterval(function(){
			timerCTX.clearRect(0,0,timer.width,timer.height);
			today = new Date();
			//difference=((launchDate-today)/(startDate-launchDate));
            difference+=.01;
			//console.log(difference)
			displayTime(difference);
		},50);