I had several apps running under Chrome on a Windows 10 PC. It stopped working so I reinstalled leaflet but it still doesn’t work. Using Chrome Developer Tools, it stops in leaflet.js at

I have five markers: one for the center (coordinates: 0,0), and four for each side with coordinates:
(1, 1) (1, -1) (-1, 1) (-1, -1)
I’m attempting to adjust the map to display all markers at the center.