Moving average in JS

ma.js

function movingAvg(series, len) {
  var ret = [];
  series.forEach(function(elem, i, ser) {
    var localSeries = ser.slice(0, i+1), lsLen = localSeries.length
    
    len && localSeries.splice( 0, Math.max(0, lsLen-len) );
            
    ret.push(
      Math.round(
        localSeries.reduce(
          function(a,b){return a+b;},
          0
        )/localSeries.length
      )
    );
  });

  return ret;
}

Moving average is used in charting to smoothen curves and show trends. If you think about a graph created form a typical data series, it tends to have spikes and dips that seem very random. MA can smoothen it and help show underlying trends. MA is used in technical analysis of share price, typical signal to buy is the price going above MA, and sell is price going below MA. See example: http://jsbin.com/asalur/1