@orbit/utils/src/eq.ts

Core utilities for Orbit.

/* eslint-disable @typescript-eslint/explicit-module-boundary-types, eqeqeq, no-eq-null, valid-jsdoc */

/**
 * `eq` checks the equality of two objects.
 *
 * The properties belonging to objects (but not their prototypes) will be
 * traversed deeply and compared.
 *
 * Includes special handling for strings, numbers, dates, booleans, regexes, and
 * arrays
 */
export function eq(a: any, b: any): boolean {
  // Some elements of this function come from underscore
  // (c) 2009-2013 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
  //
  // https://github.com/jashkenas/underscore/blob/master/underscore.js

  // Identical objects are equal. `0 === -0`, but they aren't identical.
  // See the [Harmony `egal` proposal](http://wiki.ecmascript.org/doku.php?id=harmony:egal).
  if (a === b) {
    return a !== 0 || 1 / a == 1 / b;
  }
  // A strict comparison is necessary because `null == undefined`.
  if (a == null || b == null) {
    return a === b;
  }

  let type = Object.prototype.toString.call(a);
  if (type !== Object.prototype.toString.call(b)) {
    return false;
  }

  switch (type) {
    case '[object String]':
      return a == String(b);
    case '[object Number]':
      // `NaN`s are equivalent, but non-reflexive. An `egal` comparison is performed for
      // other numeric values.
      return a != +a ? b != +b : a == 0 ? 1 / a == 1 / b : a == +b;
    case '[object Date]':
    case '[object Boolean]':
      // Coerce dates and booleans to numeric primitive values. Dates are compared by their
      // millisecond representations. Note that invalid dates with millisecond representations
      // of `NaN` are not equivalent.
      return +a == +b;
    // RegExps are compared by their source patterns and flags.
    case '[object RegExp]':
      return (
        a.source == b.source &&
        a.global == b.global &&
        a.multiline == b.multiline &&
        a.ignoreCase == b.ignoreCase
      );
  }
  if (typeof a != 'object' || typeof b != 'object') {
    return false;
  }

  if (type === '[object Array]') {
    if (a.length !== b.length) {
      return false;
    }
  }

  let i;
  for (i in b) {
    if (b.hasOwnProperty(i)) {
      if (!eq(a[i], b[i])) {
        return false;
      }
    }
  }
  for (i in a) {
    if (a.hasOwnProperty(i)) {
      if (!eq(a[i], b[i])) {
        return false;
      }
    }
  }
  return true;
}