compare2Objects.js

static compare2Objects(x, y) {
    const leftChain = [];
    const rightChain = [];
    let p;
    // remember that NaN === NaN returns false
    // and isNaN(undefined) returns true
    if (isNaN(x) && isNaN(y) && typeof x === 'number' && typeof y === 'number') {
      return true;
    }
    // Compare primitives and functions.
    // Check if both arguments link to the same object.
    // Especially useful on the step where we compare prototypes
    if (x === y) {
      return true;
    }
    // Works in case when functions are created in constructor.
    // Comparing dates is a common scenario. Another built-ins?
    // We can even handle functions passed across iframes
    if ((typeof x === 'function' && typeof y === 'function') ||
      (x instanceof Date && y instanceof Date) ||
      (x instanceof RegExp && y instanceof RegExp) ||
      (x instanceof String && y instanceof String) ||
      (x instanceof Number && y instanceof Number)) {
      return x.toString() === y.toString();
    }
    // At last checking prototypes as good as we can
    if (!(x instanceof Object && y instanceof Object)) {
      return false;
    }
    if (x.isPrototypeOf(y) || y.isPrototypeOf(x)) {
      return false;
    }
    if (x.constructor !== y.constructor) {
      return false;
    }
    if (x.prototype !== y.prototype) {
      return false;
    }
    // Check for infinitive linking loops
    if (leftChain.indexOf(x) > -1 || rightChain.indexOf(y) > -1) {
      return false;
    }
    // Quick checking of one object being a subset of another.
    // todo: cache the structure of arguments[0] for performance
    for (p in y) {
      if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
        return false;
      }
      else if (typeof y[p] !== typeof x[p]) {
        return false;
      }
    }
    for (p of Object.keys(x)) {
      if (y.hasOwnProperty(p) !== x.hasOwnProperty(p)) {
        return false;
      }
      else if (typeof y[p] !== typeof x[p]) {
        return false;
      }
      switch (typeof (x[p])) {
        case 'object':
        case 'function':
          leftChain.push(x);
          rightChain.push(y);
          if (!this.compare2Objects(x[p], y[p])) {
            return false;
          }
          leftChain.pop();
          rightChain.pop();
          break;
        default:
          if (x[p] !== y[p]) {
            return false;
          }
          break;
      }
    }
    return true;
  }