JSFiddle - React, Tailwind, and code Playground

JavaScript

var data = [
    [0, 0],
    [1, 1],
    [2, 2],
    [3, 3]
];

var movingWindowAvg = function(arr, step) {
        return arr.map(function(_, idx) { 
          _=_[1];
          var wnd = arr.slice(idx - step, idx + step + 1); 
          alert('wnd: ' + wnd);
          var result = d3.sum(to1D(wnd)) / wnd.length;
          if (isNaN(result))
          { 
              result = _; 
              alert('not a res ' + _);
          }
          return result;
        });
};
console.log(movingWindowAvg(data, 1));

function to1D(wnd)
{
    var nwnd = new Array();
    for(var i = 0; i < wnd.length; i++)
    {
         nwnd.push(wnd[i][1]); //1 to access value   
    }
    return nwnd;
    
}