Given two points in a 2D plane, you can calculate the midpoint between them by averaging the x and y coordinates of the two points. This is a simple operation that can be done in a single line of code.

Midpoint in 2D space

First off, you can use array destructuring to extract the x and y coordinates of the two points from the input arrays. Then, you can calculate the midpoint for each dimension by adding the two endpoints and dividing the result by 2.

const midpoint = ([x1, y1], [x2, y2]) => [(x1 + x2) / 2, (y1 + y2) / 2];

midpoint([2, 2], [4, 4]); // [3, 3]
midpoint([4, 4], [6, 6]); // [5, 5]
midpoint([1, 3], [2, 4]); // [1.5, 3.5]

Midpoint in 3D space

This operation can be easily to extended to 3D space by adding a third dimension to the input arrays and the output array.

const midpoint3D = ([x1, y1, z1], [x2, y2, z2]) => [
  (x1 + x2) / 2,
  (y1 + y2) / 2,
  (z1 + z2) / 2,
];

midpoint3D([2, 2, 2], [4, 4, 4]); // [3, 3, 3]
midpoint3D([4, 4, 4], [6, 6, 6]); // [5, 5, 5]
midpoint3D([1, 3, 5], [2, 4, 6]); // [1.5, 3.5, 5.5]

Midpoint in N-dimensional space

In fact, you can extend this operation to any number of dimensions by adding more elements to the input arrays and the output array. The formula remains the same, but you will have to use Array.prototype.map() to iterate over the coordinates of the two points.

const midpointND = (point1, point2) =>
  point1.map((coord, i) => (coord + point2[i]) / 2);

midpointND([2, 2, 2], [4, 4, 4]); // [3, 3, 3]
midpointND([4, 4, 4, 4], [6, 6, 6, 6]); // [5, 5, 5, 5]
midpointND([1, 3, 5, 7, 9], [2, 4, 6, 8, 10]); // [1.5, 3.5, 5.5, 7.5, 9.5]