How to fix field name is undefined error?

604

December 26, 2016, at 03:06 AM

I have this Javascript code to sort strings but I get error a.k is undefined

var dataset = [{
  "field1": "dfg34r",
  "field2": "sdfsd"
}, {
  "field1": "d3f32dg",
  "field2": "fgjfgj"
}, {
  "field1": "fdbhjjts",
  "field2": "hswer"
}, {
  "field1": "dfg4r",
  "field2": "ghje"
}, {
  "field1": "fgsdfwe",
  "field2": "dhfke"
}];
function sort_col(evt){
  var k = evt.target.innerText; //k = clicked field name field1 or field2
    dataset.sort(function (a, b) {      
      var nameA = a.k.toUpperCase(); // error here a.k is undefined
      var nameB = b.k.toUpperCase(); 

      if (nameA < nameB) {
        return -1;
      }
      if (nameA > nameB) {
        return 1;
      }
      // names must be equal
      return 0;   
    }); 
  }

if I removed toUpperCase the code work normally so how I can fix this error and be able to convert string to upper case ?

Answer 1

You have to use bracket notation at this context instead of a dot notation,

var nameA = a[k]toUpperCase(); 
var nameB = b[k]toUpperCase();

If you use dot notation, then property look up over objects a and b will happen for the property k, not the value which resides inside that.

Answer 2

I think modifying the code like below should solve the undefined problem.

  function sort_col(evt){
   var k = evt.target.innerText; //k = clicked field name field1 or field2
  dataset.sort(function (a, b) {
  var nameA = "";
  var nameB = "";     
  if(k=="field1"){
  nameA = a.field1.toUpperCase(); // error here a.k is undefined
  nameB = b.field1.toUpperCase();
   }  else{
  nameA = a.field2.toUpperCase(); // error here a.k is undefined
  nameB = b.field2.toUpperCase();
 }

  if (nameA < nameB) {
    return -1;
  }
  if (nameA > nameB) {
    return 1;
  }
  // names must be equal
  return 0;   
});

}

It is giving undefined for a.k as it will not be able to replace the value of k dynamically during the a.k.toUpperCase evaluation.