Get file type from array buffer(based on hexadecimal/magic-number value)

index.js

function getImageType(arrayBuffer){
      var type = "";
      var dv = new DataView(arrayBuffer,0,5);
      var nume1 = dv.getUint8(0,true);
      var nume2 = dv.getUint8(1,true);
      var hex = nume1.toString(16) + nume2.toString(16) ;
 
      switch(hex){
          case "8950":
              type = "image/png";
              break;
          case "4749":
              type = "image/gif";
              break;
          case "424d":
              type = "image/bmp";
              break;
          case "ffd8":
              type = "image/jpeg";
              break;
          default:
              type = null;
              break;
      }
      return type;
  }