code: function ( iterable = null ) {
  
  	this.front = null ;
  	this.back = null ;
  	this.length = 0 ;
  
  	if ( iterable !== null ) {
  
  		for ( let value of iterable ) this.push( value ) ;
  
  	}
  
  }
docs: Doubly linked list implementation
  making use of dummy nodes for the
  sake of simplicity.