This function scales the given value from one domain to another. scale( [a,b] , [min,max] , a ) = min AND scale( [a,b] , [min,max] , b ) = max

Scale.js

var scale = function (sourceDomain, targetDomain, x) {
        var sourceMin = sourceDomain[0];
        var sourceMax = sourceDomain[1];

        var targetMin = targetDomain[0];
        var targetMax = targetDomain[1];

        return {
          value: (((targetMax - targetMin) * (x - sourceMin)) / (sourceMax - sourceMin)) + targetMin,
          scalingFactor: (targetMax - targetMin) / (sourceMax - sourceMin)
        }
      };