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度比较，尤其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，但我正在努力了解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 :) 我将不胜感激您在改进代码方面可能获得的任何提示和帮助，如果您能帮助我更好地理解需要发生的递归。提前致谢!

• 问题(Eloquent JS 第 2 版，第 4 章，练习 4):

  Write a function, deepEqual, that takes two values and returns true only if they are the same value or are objects with the same properties whose values are also equal when compared with a recursive call to deepEqual.

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. 
      }
    }

最佳答案

可能最简单的方法是发布一个功能，该功能可以完成带有大量评论的工作。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 Date、RegExp、Error 等测试可能应该返回 false，然后进行属性检查，但只有当您认为有人可能将属性附加到 Number 对象时才这样做(很少使用 Number 对象，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;
}

关于JavaScript:递归深度比较:对象和属性，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30476150/