Object.prototype extensions for JavaScript

object.prototype.js

Object.prototype[Symbol.iterator] = function () {
  let i = 0;
  const keys = Object.keys(this);
  return {
    next: () => {
      return {
        value: [keys[i], this[keys[i++]]],
        done: i > keys.length,
      };
    },
  };
};

Object.prototype.reduce = function (reducer, init) {
  let acc = init;
  for (const [key, value] of this) {
    acc = reducer(acc, value, key, this);
  }
  return acc;
};

Object.prototype.map = function (mapper) {
  return this.reduce((acc, value, key) => {
    acc[key] = mapper(value, key, this);
    return acc;
  }, {});
};

Object.prototype.filter = function (pred) {
  return this.reduce((acc, value, key) => {
    if (pred(value, key, this))
      acc[key] = value;
    return acc;
  }, {});
};

Object.prototype.find = function (pred) {
  for (const [key, value] of this) {
    if (pred(value, key, this)) return value;
  }
};

Object.prototype.findKey = function (pred) {
  for (const [key, value] of this) {
    if (pred(value, key, this)) return key;
  }
};

Object.prototype.findPair = function (pred) {
  for (const [key, value] of this) {
    if (pred(value, key, this)) return [key, value];
  }
};

const obj = { a: 10, b: 20 };

for (const item of obj) {
  console.log(item);
  // [ "a", 10 ]
  // [ "b", 20 ]
}

console.log(obj.map(x => x * 2)); // { a: 20, b: 40 }
console.log(obj.filter(x => x > 10)); // { b: 20 }
console.log(obj.find(x => x > 10)); // 20
console.log(obj.findKey(x => x > 10)); // 'b'
console.log(obj.findPair(x => x > 10)); // [ 'b', 20 ]