Given the 3 points of a quadratic curve the following function returns the length.
function quadraticBezierLength(x1,y1,x2,y2,x3,y3)
var a, e, c, d, u, a1, e1, c1, d1, u1, v1x, v1y;
v1x = x2 * 2;
v1y = y2 * 2;
d = x1 - v1x + x3;
d1 = y1 - v1y + y3;
e = v1x - 2 * x1;
...