Leaflet only loads one tile

I have a problem with Leaflet that actually holds up my whole work. For some reasons I can not explain, the UI of Leaflet is correctly loaded in my Intel XDK app, but there is only one map tile loaded - the same code works in another test app! Now, that I tried everything I could do, I hope that someone here can solve my problem.

For better understanding, here is the code in my leaflet.js (it isn't the leaflet.js, because I'm using the leaflet-src.js as script) and a screenshot of the map window of the app.

function initLeaflet() {
document.getElementById("map").setAttribute("style", "height:" + window.innerHeight + "px; width:" + window.innerWidth + "px;");
var map = L.map('map');

L.tileLayer('https://{s}.tiles.mapbox.com/v3/{id}/{z}/{x}/{y}.png', {
    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: 'examples.map-i875mjb7'
}).addTo(map);

map.on('locationfound', onLocationFound);
map.on('locationerror', onLocationError);

map.locate({setView: true, maxZoom: 16});

map.on('click', onMapClick);
}

function onLocationFound(e) {
var radius = e.accuracy / 2;

L.marker(e.latlng).addTo(map)
.bindPopup("Position: " + e.latlng + " Genauigkeit " + radius ).openPopup();

L.circle(e.latlng, radius).addTo(map);
}

function onLocationError(e) {
alert(e.message);
}


function onMapClick(e) {
marker = new L.marker(e.latlng, {id:uni, icon:redIcon, draggable:'true'});
marker.on('dragend', function(event){
    var marker = event.target;
    var position = marker.getLatLng();
    alert(position);
    marker.setLatLng([position],{id:uni,draggable:'true'}).bindPopup(position).update();
});
map.addLayer(marker);
}     

//var x = document.getElementById("demo");

function getLocation() {
if (navigator.geolocation) {
    navigator.geolocation.getCurrentPosition(showPosition);
} else { 
    //x.innerHTML = "Geolocation is not supported by this browser.";
}
}

function showPosition(position) {
//x.innerHTML = "Latitude: " + position.coords.latitude + 
//"<br>Longitude: " + position.coords.longitude;    
}

https://i.sstatic.net/X39H1.jpg

I would guess that the size of the map upon initialization is the culprit.

Leaflet needs to know the size of the element it is embedded in when initializing. Leaflet uses that information to know how much tiles to load etc. Furthermore any programmatic changes (or changes that cannot be easily detected by Leaflet) to the size of the map have to be followed by map.invalidateSize(..) link.

I suspect that after you set the size, Leaflet fails to read properly the new size of the #map element. Try invalidating the size afterwards or run initialization asynchronously. I would add:

setTimeout(function () {
    map.invalidateSize();
}, 0);

and check if it gets any better.