Predict the next value in a 2nd order polynomial sequence with Javascript

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Javascript

mathematics

I'd like to give a Javascript function an array and then extrapolate forwards by a number of periods -

eg

var numArray = [0,1,2,3,4,5]

var myFunction = function(array,period){}

So myFunction(numArray,7) would return '6' and myFunction(numArray,8) would return '7'

I think I can make this work for a linear least squares, but how would I make it work for a 2nd degree polynomial?

Thank you

MV