Hey! This is really neat-- I ran into the same issue and used the snippet of your code to layout the items in my CSS Grid properly.

I also wrote some unit tests, if you'd like to use them.

describe('reorder', function () {
    it('should reorder successfully when rows are divisible', function () {
      const initialArray = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];
      const endArray = [0, 3, 6, 9, 1, 4, 7, 10, 2, 5, 8, 11];
      expect(reorder(initialArray, 3)).to.have.ordered.members(endArray);
    });
    it('should reorder successfully when rows are not evenly divisible', function () {
      const initialArray = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
      const endArray = [0, 3, 6, 9, 1, 4, 7, 10, 2, 5, 8];
      expect(reorder(initialArray, 3)).to.have.ordered.members(endArray);
    });
    it('should return the same array if num columns are less than array length', function () {
      const initialArray = [0, 1, 2, 3, 4];
      const endArray = [0, 1, 2, 3, 4];
      expect(reorder(initialArray, 5)).to.have.ordered.members(endArray);
    });
  });

It might sth unescaped, like

`layout` + `${...}` 

coz i guess the plus is not need there, right?

The order will break if more items added to array.
You could add this functionality, it's very convenient for lazyload (load more).

Card positions are off on chrome (71), and ie11

When using, for example, a "show more" button at the bottom of the masonry layout, and then AJAX loading additional items in, the original items all get shuffled out of place.

Perhaps this is a limitation of using the multicolumn layout? A possible work-around might be to reorder all images together, then remove and re-add all items? That seems very inefficient and could cause paint/resource issues though. Any thoughts?

Hello, you have a version that is not react, in addition to only having 1 js file, 1 css, 1 html, with that it would be easier to understand, I await your prompt response.

In your example if item 1, 4, 7 and 10 have big size, then the first column will be very high.
How to solve this issue?