Angular JS: Cannot read property 'then' of undefined

Inside the "if" you are returning "true" and outside the "if" you are returning nothing so you cannot use the return of clearBefore() as a promise.

Maybe this is what you want:

function clearBefore(val) {
  if (val.isEnrolled && val.name === 'XYZ') {   
    return $q.resolve(vm.clear(val, 'Hello'));
  }

  return $q.reject();
}

clearBefore(val).then(
  function(val) {
    console.log('ok', val);
  },
  function() {
    console.log('not ok...');
  }
);

Now every return point of the function returns a promise. We have a $q.resolve() inside the "if" and a $q.reject() outside to return a failed promise.

You need to return your promise

function clearBefore(val){
     if (val.isEnrolled && val.name === 'XYZ')
     {   
         return vm.clear(val, 'Hello').then(function(value)
         { 
              return value; 
         }); 
         return true; 
      } 
}

something like this

It seems that you don't return anything at the end of the clearBefore() function, so try to do so:

function clearBefore(val) {
                if (val.isEnrolled && val.name === 'XYZ') {
                    vm.clear(val, 'Hello').then(function(value){
                        return value;
                    });
                }
              return val; // here you should return what you need
            }

and after that this:

clearBefore(val).then(function (returnVal) {});

To resolve the issue i did something like following (introduced promise to the function)

function clearOTPBefore(page) {
                return $q(function (resolve, reject) {
                    if (val.isEnrolled && val.name === 'XYZ') {
                        return vm.clear(val, 'Hello').then(function(value){
                            return resolve(value);
                        });
                    } else {
                        resolve(true);
                    }

                })
            }