JSFiddle - React, Tailwind, and code Playground

HTML

<div id="demo"></div>

JavaScript

var employees =[
    {id: 1, name: 'name'},
    {id: 2, name: 'name 1'},
    {id: 3, name: 'name 2'},
    {id: 5, name: 'name 4'}
];

var commonUtils = {

  isExistName: function(_name, _collection, _prop) {
  
    for(var i = 0; i< _collection.length; i++){

      if(_collection[i][_prop].localeCompare(_name)==0){

        return true;
      }

    }

      return false;
  },
  
  generateNewName: function(_name, _collection, _prop){
    var i = 1;
    var searching = true;
    while (searching) {
      var newName = _name+ " " + i;
      if (!this.isExistName(newName, _collection, _prop)) {
        return newName;
      }
      i++;
    };
  }

};

document.getElementById("demo").innerHTML = "newName: " + commonUtils.generateNewName("name", employees, 'name')