hex-grid.js

const range = require('lodash.range');
const flatMap = require('lodash.flatmap');
const root3by2 = Math.sqrt(3) / 2;

module.exports = ({rows, cols, size = 1, map = a => a}) => flatMap(
  range(rows),
  row => range(cols).map(
    col => map([
      row % 2
        ? col * size
        : size / 2 + col * size,
      row * size * root3by2,
    ])
  )
);