Check duplicates in an array by property and mark duplicates with a boolean flag.

check-duplicates-in-array-by-property.js

const myArray = [
  {id: 1, name: 'Abhinav', email: 'abhinav@gmail.com'},
  {id: 2, name: 'Aviral', email: 'aviral@gmail.com'},
  {id: 3, name: 'Jitendra', email: 'jitendra@gmail.com'},
  {id: 4, name: 'Rajesh', email: 'rajesh@gmail.com'},
  {id: 5, name: 'Abhinav', email: 'abhinav.nigam@gmail.com'},
  {id: 6, name: 'Akash', email: 'akash@gmail.com'},
];
let arrayCopy = JSON.parse(JSON.stringify(myArray));


function checkDuplicates(propertyName, inputArray) {
  let duplicateFound = false,
      testObject = {};

  inputArray.map(function(item) {
    var itemPropertyName = item[propertyName];    
    if (itemPropertyName in testObject) {
      testObject[itemPropertyName].duplicate = true;
      item.duplicate = true;
      duplicateFound = true;
    }
    else {
      testObject[itemPropertyName] = item;
      delete item.duplicate;
    }
  });
  
  return duplicateFound;
}


console.log('The Array before processing: ', myArray);
console.log('Duplicates found in the array: '+ checkDuplicates('name', arrayCopy));
console.log('The Array after processing: ', arrayCopy );