Как сгенерировать динамический идентификатор для объекта JavaScript при вставке нового элемента?

var contacts =[{"id":1,"first":"Mike","last":"Johnson","email":"[email protected]","phone":"(203) 567-9055","status":1},{"id":2,"first":"John","last":"Dunn","email":"[email protected]","phone":"(319) 451-7889","status":1},{"id":3,"first":"Lisa","last":"Morgan","email":"[email protected]","phone":"(508) 233-8908","status":1},{"id":4,"first":"Dave","last":"Hart","email":"[email protected]","phone":"(509) 874-9411","status":1}];

// just a quick dirty conversion
let obj = contacts.reduce((a, c) => (a[c.id] = c, a), {})

//Object looks like:
console.log(obj)

// find the largest key // maybe a good way to decide the next key
largest_id = Math.max(...Object.keys(obj))
console.log("largest ID", largest_id)

// is ID 4 taken?
console.log("is there a 4", 4 in obj) //yes
// alternatively obj.hasOwnProperty('4')

// is 5?
console.log("is there a 5", 5 in obj) //no

// update ID 4:
obj['4'].first = "Mark"
console.log(obj['4'])

var contacts  = {

   
  1: {
    first: "Mike",
    last: "Johnson",    
    email:"[email protected]",
    phone:"(203) 567-9055",
    status:"1"
 },
  2: {
    first: "John",
    last: "Dunn",    
    email:"[email protected]",
    phone:"(319) 451-7889",
    status:"1"
 },
  3: {
    first: "Lisa",
    last: "Morgan",    
    email:"[email protected]",
    phone:"(508) 233-8908",
    status:"1"
 },
  4: {
    first: "Dave",
    last: "Hart",    
    email:"[email protected]",
    phone:"(509) 874-9411",
    status:"1"
 }
};

var frmKey = 5;
if(contacts[frmKey]){
console.log(contacts[frmKey]);
 // If already exist in array then update object
}else{
  contacts[frmKey] = {first: "Lisa1",last: "Morgan1", email:"[email protected]", phone:"(508) 233-8908", status:"1" };

  console.log("Added New Key::"+frmKey,contacts[frmKey]);

}

const collection = {};

function insert(obj){
   // if id is set in object and object is already in Collection... 
   if(obj.id && collection.hasOwnProperty(obj.id) ){ 
     // Update object!
     collection[obj.id]= Object.assign(collection[ obj.id], obj) ;
   }else{ 
     // if provided object has no ID... generate it!
     if( !obj.id ) obj.id = Object.keys(collection).length;
     // insert provided object to collection;
     collection[obj.id]= obj;
   }
   // return generaed id;
   return obj.id;
}


// Let's test...

let obj_1 ={"first":"Mike","last":"Johnson","email":"[email protected]","phone":"(203) 567-9055","status":1};

let obj_2 = {"first":"John","last":"Dunn","email":"[email protected]","phone":"(319) 451-7889","status":1};

// insert bth object
insert(obj_1);
insert(obj_2);
// perform a change in object 2
obj_2.first ='Joseph';
// insert object 2 again...
insert(obj_2);
// object 2 has been updated, and all have unique ids
console.log(collection);