I have a Leaflet map in default projection and a wms layer also in default (web mercator) projection. I would like to add polylines and a geoJSON layer to my map, but the coordinates are in EPSG4326. I have figured out how to set the entire map projection, passing L.CRS.EPSG4326 into the map object. But as I have a WMS in web mercator (no other projection options here), but polylines and geoJSON in EPSG4326, that does not seem to be an option. I looked at the Proj4Leaflet plugin, but that also seems to pass a CRS into the map object. Any ideas? Thanks
Lealfet expects GeoJSON to be in EPSG:4326. In fact, the entire API uses 4326 (lat/lng), so you are good to go without any reprojection.
If you need to reproject GeoJSON, you could look at https://github.com/perliedman/reproject.