d3-2d-binning.js

var histWidth = 2; // Number of bins in x
var histHeight = 2; // Number of bins in y
var pointWidth = 5; // Number of points in x
var pointHeight = 5; // Number of points in y

var xScale = d3.scale.quantile()
                     .domain([0, pointWidth-1])
                     .range([0, histWidth-1]);
var yScale = d3.scale.quantile()
                     .domain([0, pointHeight-1])
                     .range([0, histHeight-1]);

/* Returns the boundaries of bin x, y in the data */
function getBin(x, y) {
    return [xScale.invertExtent(x), yScale.invertExtent(y)];
}

console.log(getBin(0,0));