Convert object array to hash map, indexed by an attribute value of the Object

Question

Use Case

The use case is to convert an array of objects into a hash map based on string or function provided to evaluate and use as the key in the hash map and val

Answer 1

try

let toHashMap = (a,f) => a.reduce((a,c)=> (a[f(c)]=c,a),{});

let arr=[
  {id:123, name:'naveen'}, 
  {id:345, name:"kumar"}
];

let fkey = o => o.id; // function changing object to string (key)

let toHashMap = (a,f) => a.reduce((a,c)=> (a[f(c)]=c,a),{});

console.log( toHashMap(arr,fkey) );

// Adding to prototype is NOT recommented:
//
// Array.prototype.toHashMap = function(f) { return toHashMap(this,f) };
// console.log( arr.toHashMap(fkey) );