javascript - Adding dynamic mean to time series chart -

i try explain problem accurate possible. looking javascript chart library filling 2 following conditions:

from ajax request retrieving time series,  display dynamically data when changing time window. 

such done on highstocks: http://www.highcharts.com/stock/demo/basic-line

and

plot horizontal line corresponding mean,  changing when user update time window on chart. 

actually possible display horizontal line. fixed on whole data , not change accordingly when time window modified:

http://www.highcharts.com/stock/demo/yaxis-plotlines

i quite new topic , know if it'sp ossible modify highstock classes have such result. or maybe other js libraries exists?

using combination of answer here:

• highchart, total of visible series data after setextremes

and example of dynamic average using visible series made previous question, here:

• http://jsfiddle.net/jlbriggs/gweulegq/

i put example, using aftersetextremes event, this:

xaxis      : {              events:{                 aftersetextremes:function() {                     var ext = this.getextremes();                   getaverage(this.chart, ext.min, ext.max, show, width, avgcolor, dashstyle);                                 }             }         }, 

working example here:

• http://jsfiddle.net/jlbriggs/c93543yl/

the idea is:

1) capture aftersetextremes event

2) resulting axis min , max

3) loop through series data

4) if point between min , max, increment count, , add point's y value sum

5) calculate average accordingly, check existence of average series, if exists, update, if not, add

it use plot line add/remove needed instead of series, having series has legend entry.