为何JavaScript对象无法用.sort排序，数组内对象却可以？

Great question—this cuts right to the core of how JavaScript handles different data collections. Let’s break this down in plain terms:

1. The Core Design Difference Between Objects and Arrays #

First, remember what each structure is built for:

• Objects: They’re key-value pair collections, originally designed for lookup (mapping unique keys to values) rather than maintaining a strict sequence. While modern JS preserves insertion order for object keys, this is a side effect, not a core feature. Objects don’t exist to be rearranged like ordered lists.
• Arrays: They’re explicitly ordered lists, indexed by sequential integers (0, 1, 2...). Their entire purpose is to manage ordered data, which is why native methods like .sort(), .shift(), and .splice() exist specifically for arrays.

2. Why .sort() Works for Arrays (But Not Objects) #

The .sort() method is built exclusively for ordered collections. Here’s how it operates:

• It iterates over elements using their numeric array indices.
• It uses your custom comparison function to compare pairs of elements side-by-side.
• It rearranges the elements in the array’s underlying ordered list based on those comparisons.

Objects have no built-in ordered element list to iterate over or rearrange. Even if you can loop through an object’s keys/values, the object itself doesn’t expose a way to reorder its key-value pairs directly—there’s no equivalent to swapping positions like you can with array indices.

3. Your Example in Action #

Let’s use your code to make this concrete:

• Your original query object:

  var query = { 
    "736":{ ns: 42, pageid: 12, lang: "en", index: 3 }, 
    "421":{ ns: 12, pageid: 36, lang: "en", index: 4 }, 
    "102":{ ns: 2, pageid: 19, lang: "en", index: 1 } 
  };
  

  This is a set of key-value pairs where the keys are strings ("736", "421", etc.). Even if you want to sort by the index property of the values, the object has no way to reorder these pairs as part of its structure—it’s not built for that.

• When you convert it to queryArr:

  var queryArr = [
    {ns: 42, pageid: 12, lang: "en", index: 3}, 
    {ns: 12, pageid: 36, lang: "en", index: 4}, 
    {ns: 2, pageid: 19, lang: "en", index: 1}
  ];
  

  Now you have an ordered list where each element is one of the original objects. The array’s indices (0, 1, 2) give .sort() a clear way to access and compare elements. When you run:

  queryArr.sort(function(i,j){ return j.index - i.index; });
  

  The method compares each pair of objects (using their index property) and rearranges them in the array’s ordered list—something the original object can’t do because it lacks that inherent ordered structure.

To put it simply: Arrays are built for ordered operations like sorting, while objects are built for key-based lookups. Converting an object’s values to an array lets you leverage the array’s native sorting capabilities to arrange the objects exactly how you want.

内容的提问来源于stack exchange，提问作者firefiber