How to convert extent from EPSG 3857 to EPSG 3826

Question

I have a problem about transformation from EPSG:4326 to EPSG:3826 in using geojson-vt. In general, I could using the following statement to get the correct slices from performing function in geojson-vt.

var tileOptions = {
        maxZoom: 24, 
        extent: 4096,
        buffer: 64,  
        indexMaxPoints: 100000, 
    };
 
var tileIndex = geojsonvt(geoJson, tileOptions);

And the problem is when it come to use proj4.js to project EPSG:4326 to EPSG:3826 in leaflet.js, the things will be different. And what is the correct option to make in such a case, how to get the correct extent value when projecting from EPSG:4326 to EPSG:3826, thanks a lot.