Leaflet minZoom based on screen resolution. Fit up to one globe.

leaflet-min-zoom-res-based.js

// Get the largest screen dimension 
// reason for doing this is a phone may start in portrait then move to landscape
var maxScreenDimension = window.innerHeight > window.innerWidth ? window.innerHeight : window.innerWidth;

// assuming tiles are 256 x 256
var tileSize = 256;

// How many tiles needed to for the largest screen dimension
// I take the floor because I don't want to see more then 1 world
// Use Math.ceil if you don't mind seeing the world repeat
var maxTiles = Math.floor(maxScreenDimension / tileSize);

/* MATH MAGIC !!!!!

    number of tiles needed for one side = 2 ^ zoomlevel
    or
    maxTiles = 2 ^ zoomlevel

    Time to show my steps! assuming log base 2 for all steps
    
    log(2 ^ zoomlevel) = log(maxTiles)

    properties of logs
    zoomlevel * log(2) = log(maxTiles)

    log base 2 of 2 is just 1
    zoomlevel * 1 = log(maxTiles)

    JS Math.log is ln (natural log) not base 2
    So we need to use another log property

    Math.log(maxTiles) / Math.log(2) = Log base 2 of maxTiles
*/

// I am taking the ceiling so I don't see more then 1 world
// Use Math.floor if you don't mind seeing the world repeat
minZoom = Math.ceil(Math.log(maxTiles) / Math.log(2));

// only let minZoom be 2 or higher
minZoom = minZoom < 2 ? 2 : minZoom;
                
// plug this into L.map() options
L.map('map', {
    // ...
    minZoom: minZoom
    // ...
});

I'm also assuming that we can precalculate this given a list of breakpoints right? Lets say I only care about supporting 5 difference screen sizes

Only place that takes in screen size is line 3:

var maxScreenDimension = window.innerHeight > window.innerWidth ? window.innerHeight : window.innerWidth;

Screen size is grabbed dynamically from the device. Add some if statements if you want to only grab for certain screen sizes!

See:
https://developer.mozilla.org/en-US/docs/Web/API/Window/innerWidth
https://developer.mozilla.org/en-US/docs/Web/API/Window/innerHeight