New Twiddle

controllers.application.js

export default Ember.Controller.extend({
  
  center: L.latLng(56, 10.3),
	zoom: 7,
  
  statusText: Ember.computed('center', function() {
    var c = this.get('center');
    return c ? `${c.lat}, ${c.lng}` : '';
  }),
    
  actions: {
    onLoad(e) {
      var c = this.get('center');
      e.target.setView(c, 5);
    },
    updateCenter(e) {
      this.set('center', e.target.getCenter());
    }
  }
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.leaflet-container {
  	background-color: #deedff;
    width: 100%;
    height: 700px;
    font-family: inherit;
}

templates.application.hbs

{{#leaflet-map lat=56 lng=10.3 zoom=zoom onLoad=onLoad onMoveend=updateCenter}}
    {{tile-layer url="http://{s}.basemaps.cartocdn.com/light_all/{z}/{x}/{y}.png"}}
    
    {{#marker-layer location=center icon=defaultMarkerIcon}}
        {{#tooltip-layer permanent=true}}
            computed from center of map
        {{/tooltip-layer}}
    {{/marker-layer}}
{{/leaflet-map}}

{{statusText}}

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1",
    "ember-leaflet": "3.0.10"
  }
}