Javascript - Counting duplicates in object array and storing the count as a new object

Question

I have an array of javascript objects that are products. These products are displayed in a list as a cart.

I want to count the number of duplicate products in the ar

Answer 1

The easiest would be probably a map:

var map=new Map();

names.forEach(function(el){
 if(map.has(el["_id"])){
  map.get(el["_id"]).count++;
 }else{
  map.set(el["_id"],Object.assign(el,{count:1}));
 }
});  

And then recreate an array:

names=[...map.values()];

Or in old hash/array way:

var hash={},result=[];

names.forEach(function(name){
  var id=name["_id"];
  if(hash[id]){
     hash[id].count++;
  }else{
     result.push(hash[id]={
        count:1,
        ...name
     });
  }
});

console.log(result);