title: TypeError: Cannot read property '0' of undefined when comparing the arrays?
body: <p>I have a array having JSON values </p>
  
  <pre><code>category = [ {"categoryName":"abcd","productName":"chicken biriyani","price":100,"quantity":"medium"}, {"categoryName":"biriyani","productName":"mutton biriyani","price":130,"quantity":"medium"} ]
  </code></pre>
  
  <p>I have to check for the required parameters for the above category array.
  so I created a required parameters array.
  var reqarray = ['categoryName','productName','price','quantity'];</p>
  
  <p>I created the sample code for checking the values of reqarray and each value of category.But it is not working</p>
  
  <pre><code>var categoryList = [ {"categoryName":"abcd","productName":"chicken biriyani","price":100,"quantity":"medium"}, {"categoryName":"biriyani","productName":"mutton biriyani","price":130,"quantity":"medium"} ];
  for(var i in categoryList){
  
          var reqarray =['categoryName','productName','price','quantity'];
          for(var j in arr){
              if(categoryList[i].reqarray[j]=='null' || categoryList[i].reqarray[j] == " "){
                  console.log("data is null");
              }
              else if(categoryList[i].reqarray[j] == undefined){
                  console.log("required parameters");
              }
              else{
                  console.log("ok");
              }
          }
      }
  }
  </code></pre>
  
  <p>This code shows an error :</p>
  
  <pre><code>TypeError: Cannot read property '0' of undefined
  </code></pre>