JavaScript Helper Methods.js

const [dummyArray, dummyObject, dummyString, dummyNumber] = [Array, Object, String, Number];

dummyArray.prototype.merge = function (source) {
  source.forEach((element) => {
    if (!this.includes(element)) this.push(element);
  });
  return this;
};

dummyObject.prototype.deepMerge = function (source) {
  if (Array.isArray(this)) {
    this.merge(source);
    return this;
  }
  Object.entries(source).forEach(([key, value]) => {
    if (typeof this[key] === 'object') {
      this[key].deepMerge(value);
    } else {
      this[key] = value;
    }
  });
  return this;
};

dummyObject.prototype.transformIf = function (condition, lambda) {
  if (condition) {
    return lambda(this);
  }
  return this;
};

dummyObject.prototype.entries = function () {
  return Object.entries(this);
};

dummyObject.prototype.theseValues = function (...keys) {
  return keys.map(key => this[key]);
};

dummyArray.prototype.fromEntries = function () {
  return Object.fromEntries(this);
};

dummyArray.prototype.max = function (compareFn) {
  return this.reduce((acc, val) =>
    ((acc && (compareFn(val, acc) < 0)) ? acc : val), undefined);
};

dummyArray.prototype.selfMerge = function () {
  return this.reduce((acc, val) =>
    acc.deepMerge(val)
  , {});
};

dummyString.prototype.transformIf = function (condition, lambda) {
  return ((condition) ? lambda(this) : this).valueOf();
};

dummyNumber.prototype.transformIf = function (condition, lambda) {
  return ((condition) ? lambda(this) : this).valueOf();
};