FWIW, I like this smoothing function (based on ola.js):
function Smooth(f,t){var p=performance,b=p.now(),o=f,s=0,m,n,x,d,k=f;return function(v){n=p.now()-b;m=t[i]t/n/n;d=o-f;x=s[/i]t+d+d;if(n>0)k=n<t?o-x/m/t[i]n+(x+x-d)/m-s[/i]n-d:o;if(v!=void 0&&v!=o){f=k;b+=n;o=v;s=n>0&&n<t?s+3[i]x/m/t-(4[/i]x-d-d)/m/n:0}return k}}
It is very easy to use:
// Setup: initial value, milliseconds over which to smooth
var smooth = new Smooth(0, 350);
// Then later, use the smoothed value returned by this instead of the raw value:
var smoothedValue = smooth(rawValue);
It gives a smoothed value that moves to the raw value over time. It's better than the usual interpolation between a start and end value because it dynamically adjusts the curve smoothly when the raw value is changing a lot. You can see it in action here. Try changing the time from 1000 to 1500 (click Run afterward) for a more interesting demo, showing what happens when the raw value hasn't been reached yet and the raw value changes.
