foo.js

var addMarker;

$(document).ready(function(){
  var mymap = L.map('mapid').setView([35.7796, -78.6382], 13);

  L.tileLayer('https://api.tiles.mapbox.com/v4/{id}/{z}/{x}/{y}.png?access_token=pk.eyJ1IjoibWFwYm94IiwiYSI6ImNpandmbXliNDBjZWd2M2x6bDk3c2ZtOTkifQ._QA7i5Mpkd_m30IGElHziw', {
    maxZoom: 18,
    attribution: 'Map data &copy; <a href="http://openstreetmap.org">OpenStreetMap</a> contributors, ' +
      '<a href="http://creativecommons.org/licenses/by-sa/2.0/">CC-BY-SA</a>, ' +
      'Imagery © <a href="http://mapbox.com">Mapbox</a>',
    id: 'mapbox.streets'
  }).addTo(mymap);

   addMarker = function(lat, lng){
        latlng = {lat: lat, lng: lng};
        L.marker(latlng).addTo(mymap);
  }
})