I can suggest you a workaround until angular-cli get better support for 3rd party libs. It worked for me :)

First go to the project directory and type

npm install leaflet --save

then open your angular-cli-build.js and add this line

vendorNpmFiles: [
   ..................
   'leaflet/**/*.js',
    ....................
  ]

now open your src/system-config.ts, write

const map:any ={
     ..................
   'ng2-bootstrap': 'vendor/leaflet/dist',
    ....................

}

and

const packages: any = {
  'leaflet': {
    format: 'cjs'
  }

};

Open your src/index.html, add this

 <script type="text/javascript" src="vendor/leaflet/dist/leaflet.js"></script>

and dont forget to add the css file also

  <link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet/v0.7.7/leaflet.css" />

Now open your component where you want to use Leaflet

declare let L: any;
@Component({
  moduleId: module.id,
  selector: 'app-map',
  templateUrl: 'map.component.html',
  styleUrls: ['map.component.css']
})
export class MapComponent implements OnInit, AfterViewInit {
 leafletMap: any;
 ngAfterViewInit() {
    this.leafletMap = L.map("map").setView([23.709921, 90.407143], 7);
 }
}

Tada!! your map loaded :D

I can suggest you a workaround until angular-cli get better support for 3rd party libs. It worked for me :)

First go to the project directory and type

npm install leaflet --save

then open your angular-cli-build.js and add this line

vendorNpmFiles: [
   ..................
   'leaflet/**/*.js',
    ....................
  ]

now open your src/system-config.ts, write

const map:any ={
     ..................
   'leaflet': 'vendor/leaflet/dist',
    ....................

}

and

const packages: any = {
  'leaflet': {
    format: 'cjs'
  }

};

Open your src/index.html, add this

 <script type="text/javascript" src="vendor/leaflet/dist/leaflet.js"></script>

and dont forget to add the css file also

  <link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet/v0.7.7/leaflet.css" />

Now open your component where you want to use Leaflet

declare let L: any;
@Component({
  moduleId: module.id,
  selector: 'app-map',
  templateUrl: 'map.component.html',
  styleUrls: ['map.component.css']
})
export class MapComponent implements OnInit, AfterViewInit {
 leafletMap: any;
 ngAfterViewInit() {
    this.leafletMap = L.map("map").setView([23.709921, 90.407143], 7);
 }
}

Tada!! your map loaded :D