simred/src/deep/equal.js

A simple redux-like application state manager

export const equal = (x, y) => {
  if (x === y) return true; // if both x and y are null or undefined and exactly the same

  if (!(x instanceof Object) || !(y instanceof Object)) return false; // if they are not strictly equal, they both need to be Objects

  if (x.constructor !== y.constructor) return false; // they must have the exact same prototype chain, the closest we can do is
  // test there constructor.

  for (var p in x) {
    /* istanbul ignore next */
    if (!x.hasOwnProperty(p)) continue; // other properties were tested using x.constructor === y.constructor

    if (!y.hasOwnProperty(p)) return false; // allows to compare x[ p ] and y[ p ] when set to undefined

    if (x[p] === y[p]) continue; // if they have the same strict value or identity then they are equal

    if (typeof(x[p]) !== "object") return false; // Numbers, Strings, Functions, Booleans must be strictly equal

    if (!equal(x[p], y[p])) return false; // Objects and Arrays must be tested recursively
  }

  for (p in y) {
    if (y.hasOwnProperty(p) && !x.hasOwnProperty(p)) return false; // allows x[ p ] to be set to undefined
  }

  return true;
};