js深度遍历对象的属性

function optionalChaining(obj, chain) {
  	  if (obj === null || obj == undefined) {
  	  	 return 'undefined';
  	  } 
      if(!(/./g).test(chain) && obj[chain]) {
         return obj[chain];
      }
      var arr = chain.split('.');
  	  var len = arr.length,
  	      i=0;
  	  var local = '';
      
      var local = arr.shift();
      for (key in obj) {
      //	console.log(key === local && obj[key] instanceof Object )
      	if (key === local && obj[key] instanceof Object ) {
      		  return optionalChaining(obj[key], arr.join('.'));  
      	         		   		
      	}
      }
     
     return 'undefined' ;
  }