JavaScript：递归深度比较：对象和属性

Question

今天我读完了 Ch. 4 在 Eloquent JS 中，我正在努力理解如何在对象及其属性之间进行深入比较，特别是通过使用递归调用。我知道我下面的解决方案非常幼稚而且有点笨重，但我正在努力解决所有这些我仍在学习的新事物！仅仅不到一个月的编程时间 :) 我将不胜感激任何提示和帮助您改进代码，以及如果您能帮助我更好地理解需要发生的递归。提前谢谢！

• 问题（Eloquent JS 第 2 版，第 4 章，练习 4）：

  编写一个函数 deepEqual，它接受两个值并返回 true 仅当它们是相同的值或具有相同的对象时 与递归比较时其值也相等的属性 调用 deepEqual。

测试用例：

var obj = {here: {is: "an"}, object: 2};
var obj1 = {here: {is: "an"}, object: 2};
console.log(deepEqual(obj,obj1));

我的代码：

  function objectTester(x) {
      if (typeof x === 'object' && x !== null)
        return true;
    }

    function deepEqual(valOne, valTwo) {
      if (valOne === valTwo) return true;

      var comp1 = objectTester(valOne);
      var comp2 = objectTester(valTwo);

      if (comp1 === comp2) {
        var count1;
        var count2;
        for (var prop in valOne) {
            count1++
            return count1;
        }
        for (var prop in valTwo) {
            count2++
            return count2;
        }
        if (count1 === count2) {

        // This is where I'm getting stuck, not sure how I can recurisvely compare
        // two arguments that are to be compared. 
      }
    }

Answer 1

发布一个使用大量 cmets 完成工作的函数可能是最简单的。递归部分靠近底部，在传递给 every 的函数中：

// Helper to return a value's internal object [[Class]]
// That this returns [object Type] even for primitives
function getClass(obj) {
  return Object.prototype.toString.call(obj);
}

/*
** @param a, b        - values (Object, RegExp, Date, etc.)
** @returns {boolean} - true if a and b are the object or same primitive value or
**                      have the same properties with the same values
*/
function objectTester(a, b) {

  // If a and b reference the same value, return true
  if (a === b) return true;

  // If a and b aren't the same type, return false
  if (typeof a != typeof b) return false;

  // Already know types are the same, so if type is number
  // and both NaN, return true
  if (typeof a == 'number' && isNaN(a) && isNaN(b)) return true;

  // Get internal [[Class]]
  var aClass = getClass(a);
  var bClass = getClass(b)

  // Return false if not same class
  if (aClass != bClass) return false;

  // If they're Boolean, String or Number objects, check values
  if (aClass == '[object Boolean]' || aClass == '[object String]' || aClass == '[object Number]') {
    return a.valueOf() == b.valueOf();
  }

  // If they're RegExps, Dates or Error objects, check stringified values
  if (aClass == '[object RegExp]' || aClass == '[object Date]' || aClass == '[object Error]') {
    return a.toString() == b.toString();
  }

  // Otherwise they're Objects, Functions or Arrays or some kind of host object
  if (typeof a == 'object' || typeof a == 'function') {

    // For functions, check stringigied values are the same
    // Almost certainly false if a and b aren't trivial
    // and are different functions
    if (aClass == '[object Function]' && a.toString() != b.toString()) return false;

    var aKeys = Object.keys(a);
    var bKeys = Object.keys(b);

    // If they don't have the same number of keys, return false
    if (aKeys.length != bKeys.length) return false;

    // Check they have the same keys
    if (!aKeys.every(function(key){return b.hasOwnProperty(key)})) return false;

    // Check key values - uses ES5 Object.keys
    return aKeys.every(function(key){
      return objectTester(a[key], b[key])
    });
  }
  return false;
}

如果值/字符串不相同，则对 Date、RegExp、Error 等的测试可能会返回 false，然后通过属性检查，但只有在您认为有人可能会将属性附加到 Number 对象时才这样做（使用 Number 对象非常罕见，更不用说向它们添加属性了，但我想这可能会发生）。

这里是：

/*
** @param a, b        - values (Object, RegExp, Date, etc.)
** @returns {boolean} - true if a and b are the object or same primitive value or
**                      have the same properties with the same values
*/
function objectTester(a, b) {

  // If a and b reference the same value, return true
  if (a === b) return true;

  // If a and b aren't the same type, return false
  if (typeof a != typeof b) return false;

  // Already know types are the same, so if type is number
  // and both NaN, return true
  if (typeof a == 'number' && isNaN(a) && isNaN(b)) return true;

  // Get internal [[Class]]
  var aClass = getClass(a);
  var bClass = getClass(b)

  // Return false if not same class
  if (aClass != bClass) return false;

  // If they're Boolean, String or Number objects, check values
  if (aClass == '[object Boolean]' || aClass == '[object String]' || aClass == '[object Number]') {
    if (a.valueOf() != b.valueOf()) return false;
  }

  // If they're RegExps, Dates or Error objects, check stringified values
  if (aClass == '[object RegExp]' || aClass == '[object Date]' || aClass == '[object Error]') {
    if (a.toString() != b.toString()) return false;
  }

  // For functions, check stringigied values are the same
  // Almost impossible to be equal if a and b aren't trivial
  // and are different functions
  if (aClass == '[object Function]' && a.toString() != b.toString()) return false;

  // For all objects, (including Objects, Functions, Arrays and host objects),
  // check the properties
  var aKeys = Object.keys(a);
  var bKeys = Object.keys(b);

  // If they don't have the same number of keys, return false
  if (aKeys.length != bKeys.length) return false;

  // Check they have the same keys
  if (!aKeys.every(function(key){return b.hasOwnProperty(key)})) return false;

  // Check key values - uses ES5 Object.keys
  return aKeys.every(function(key){
    return objectTester(a[key], b[key])
  });
  return false;
}

Answer 2

您可以使用下面的代码进行深度比较 -

const isEqual = (a, b) => {
  if (a === b) return true;
  if (a instanceof Date && b instanceof Date) return a.getTime() === b.getTime();
  if (!a || !b || (typeof a !== 'object' && typeof b !== 'object')) return a === b;
  if (a === null || a === undefined || b === null || b === undefined) return false;
  if (a.prototype !== b.prototype) return false;
  let keys = Object.keys(a);
  if (keys.length !== Object.keys(b).length) return false;
  return keys.every(k => isEqual(a[k], b[k]));
};

示例 -

isEqual({ prop1: [2, { e: 3 }], prop2: [4], prop3: 'foo' }, { prop1: [2, { e: 3 }], prop2: [4], prop3: 'foo' }); // true

Answer 3

检查下面的代码。这应该对你有用。

function objectEquals(x, y) {
    'use strict';

    if (x === null || x === undefined || y === null || y === undefined) { return x === y; }
    // after this just checking type of one would be enough
    if (x.constructor !== y.constructor) { return false; }
    // if they are functions, they should exactly refer to same one (because of closures)
    if (x instanceof Function) { return x === y; }
    // if they are regexps, they should exactly refer to same one (it is hard to better equality check on current ES)
    if (x instanceof RegExp) { return x === y; }
    if (x === y || x.valueOf() === y.valueOf()) { return true; }
    if (Array.isArray(x) && x.length !== y.length) { return false; }

    // if they are dates, they must had equal valueOf
    if (x instanceof Date) { return false; }

    // if they are strictly equal, they both need to be object at least
    if (!(x instanceof Object)) { return false; }
    if (!(y instanceof Object)) { return false; }

    // recursive object equality check
    var p = Object.keys(x);
    return Object.keys(y).every(function (i) { return p.indexOf(i) !== -1; }) &&
        p.every(function (i) { return objectEquals(x[i], y[i]); });
}