InvertTheKey-ValuePairOfObject.js

// Write a JavaScript program to invert the key-value pairs of an object, without mutating it. The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.

const invertKeyValues = (obj, fn) => {
  return Object.keys(obj).reduce((acc, key) => {
    const val = fn ? fn(obj[key]) : obj[key];
    acc[val] = acc[val] || [];
    acc[val].push(key);
    return acc;
  }, {});
};

console.log(invertKeyValues({ a: 1, b: 2, c: 3 }));