Leaflet.EdgeBuffer 
Leaflet 1.0 plugin to support pre-loading tiles outside the current viewport on L.GridLayer-based layers.
Usage
Include Leaflet.EdgeBuffer.js. By default, a 1 tile buffer will be added beyond the viewport. To define a different buffer size use the options below.
Options
- edgeBufferTiles: (number) The number of tiles that should be loaded beyond the edge of the map viewport. This may be a fractional number. Defaults to 1.
Demos
This demo shows two maps, one without this plugin active and one with.
Limitations
This plugin does not currently work with the GoogleMutant plugin. See issues https://gitlab.com/IvanSanchez/Leaflet.GridLayer.GoogleMutant/issues/27 and https://github.com/TolonUK/Leaflet.EdgeBuffer/issues/10.
License
Leaflet.EdgeBuffer is free software and may be redistributed under the MIT License.