Create a thumbnail from an NGL stage instance

thumbnail.js

function getThumbnail(stage) {

    var canvas, context, image = new Image();

    function setupCanvas() { 
      canvas = document.createElement( 'canvas' );
      canvas.style.visibility = "hidden";
      canvas.width = 100;
      canvas.height = 100;
      document.body.append( canvas );
      context = canvas.getContext('2d');
    }

    function removeCanvas() {
      canvas.remove();
    }

    var imgPromise = stage.makeImage( { 
      trim: true,
      antialias: true,
      transparent: false });
    
    var fileDataPromise = imgPromise.then( function( blob ){

      var debug = blob;

      return new Promise( function( resolve, reject ){

        var fr = new FileReader();

        fr.onload = function() {
          resolve( this.result );
        }
        fr.readAsDataURL( blob );

      });

    });

    var resultPromise = fileDataPromise.then( function( data ){
      
      var dbg = data;
      setupCanvas();                    

      return new Promise( function( resolve, reject ){
        
        image.onload = function(  ) {
          context.clearRect(0, 0, 100, 100);
          context.drawImage( this, 0, 0, this.width, this.height, 0, 0, 100, 100 );
          resolve( canvas.toDataURL() );
        }
        image.src = data;

      });

    });

    resultPromise.then( removeCanvas );
    return resultPromise;
};