clock.js

//create a canvas object fro HTML element
var canvas = document.getElementById('canvas');
//create a 2d drawing object
var ctx = canvas.getContext('2d');
//calculate the clock radius by using the height
var radius = canvas.height / 2;
//remap the x and y axis to the center of the canvas
ctx.translate(radius, radius);
//reduce clock radius by 90%
radius = radius * 0.90;

setInterval(drawClock, 1000); //run the drawClock function every second.

function drawClock(){
    drawFace(ctx, radius);
    drawNumbers(ctx, radius);
    drawTime(ctx, radius);
}

function drawFace(ctx, radius){
    var grad;
    //draw white circle for the face
    ctx.beginPath();
    ctx.arc(0,0,radius,0,2*Math.PI);
    ctx.fillStyle = "White";
    ctx.fill();
    // create a radial gradient (inner, middle, and outer edge of clock)
    grad = ctx.createRadialGradient(0,0,radius*0.95, 0,0,radius*1.05);
    grad.addColorStop(0, '#333');
    grad.addColorStop(0.5, 'white');
    grad.addColorStop(1, '#333');
    //define gradient as stroke style
    ctx.strokeStyle = grad;
    ctx.lineWidth = radius*0.1;
    ctx.stroke(); 
    //draw the center of the clock
    ctx.beginPath();
    ctx.arc(0,0, radius*0.1,0,2*Math.PI);
    ctx.fillStyle = '#333';
    ctx.fill();
}

function drawNumbers(ctx, radius) {
    var ang;
    var num;
    ctx.font = radius*0.15 + "px arial"; //set font at 15% of radius
    ctx.textBaseline = "middle"; //set text alignment to middle
    ctx.textAlign = "center"; //set text alignment to center
    for(num=1; num < 13; num++){ //calculate the print position for each number
        ang = num *Math.PI /6;
        ctx.rotate(ang);
        ctx.translate(0, -radius*0.85);
        ctx.rotate(-ang);
        ctx.fillText(num.toString(), 0, 0);
        ctx.rotate(ang);
        ctx.translate(0, radius*0.85);
        ctx.rotate(-ang);
    }
}

function drawTime(ctx, radius){
    var now = new Date();
    var hour = now.getHours();
    var minute = now.getMinutes();
    var second = now.getSeconds();
    //hour
    hour = hour%12;
    //calculate angle of hour hand
    hour = (hour*Math.PI/6)+(minute*Math.PI/(6*60))+(second*Math.PI/(360*60));
    //make hour hand 50% of canvas's radius
    drawHand(ctx, hour, radius*0.5, radius*0.07);
    //minute
    //calculate angle of minute hand
    minute=(minute*Math.PI/30)+(second*Math.PI/(30*60));
    //make minute hand 80% of canvas's radius
    drawHand(ctx, minute, radius*0.8, radius*0.07);
    //second
    //calculate angle of second hand
    second=(second*Math.PI/30);
    //make second hand 90% of canvas's radius
    drawHand(ctx, second, radius*0.9, radius*0.02);
}

function drawHand(ctx, pos, length, width){
    ctx.beginPath();
    ctx.lineWidth = width;
    ctx.lineCap = "round";
    ctx.moveTo(0,0);
    ctx.rotate(pos);
    ctx.lineTo(0, -length);
    ctx.stroke();
    ctx.rotate(-pos);
}