HTML5 / js - how to animate straight line between two coordinates?

You could use a linear interpolation or lerp. Something like this. Here is an example on jsfiddle: http://jsfiddle.net/UtmTh/ and here is the main code:

var canvas = $("#paper")[0];
var c = canvas.getContext("2d");

var startX = 50;
var startY = 50;
var endX = 100;
var endY = 100;
var amount = 0;
setInterval(function() {
    amount += 0.05; // change to alter duration
    if (amount > 1) amount = 1;
    c.clearRect(0, 0, canvas.width, canvas.height);
    c.strokeStyle = "black";
    c.moveTo(startX, startY);
    // lerp : a  + (b - a) * f
    c.lineTo(startX + (endX - startX) * amount, 
             startY + (endY - startY) * amount);
    c.stroke();
}, 30);​

You should check this out : http://paulirish.com/2011/requestanimationframe-for-smart-animating/ it is fairly easy to do, after reading it you should be able to do it! There is also an example.

Thanks valli-R and Zevan,

I've coded an amalgam of your two answers which uses lerp with requestAnimFrame

http://jsbin.com/enobes/6