index.js
function on (el, types, fn, context) {
  types.split(' ').forEach(function (type) {
    L.DomEvent.on(el, type, fn, context)
  })
}
function on (el, types, fn, context) {
  types.split(' ').forEach(function (type) {
    L.DomEvent.on(el, type, fn, context)
  })
}
Leaflet v0.7 backwards compatibility