Nodejs 属性顺序保证

Question

注意：我使用的 Nodejs 可能与 vanilla ECMAscript 的标准有细微差别，也可能没有。

我一直听说，当使用 for-each 循环遍历对象的属性时，我不应该指望属性的顺序相同。（尽管在实践中我从未见过对象以不同顺序迭代的情况）。在生产中，我认为我们有一个拼写错误，其中创建的对象被覆盖属性.

var obj = {
  a: 'a property',
  b: 'another property',
  c: 'yet another property',
  a: 'woah we have another a?'
}

在 Nodejs 中，我是否保证包含字符串 'woah we have another a?' 的第二个属性会 ALWAYS 隐藏包含字符串的第一个属性字符串 'a property'?

Answer 1

(even though in practice I have never seen a case where the objects were iterated over in a different order) The following should give you a different order in V8 atleast.

var obj = {
  "first":"first",
  "2":"2",
  "34":"34",
  "1":"1",
  "second":"second"
};
for (var i in obj) { console.log(i); };
// Order listed:
// "1"
// "2"
// "34"
// "first"
// "second"

如讨论的那样here

ECMA-262 does not specify enumeration order. The de facto standard is to match insertion order, which V8 also does, but with one exception:

V8 gives no guarantees on the enumeration order for array indices (i.e., a property name that can be parsed as a 32-bit unsigned integer).

Remembering the insertion order for array indices would incur significant memory overhead.

虽然上面说了没有指定枚举顺序，但那是在创建对象之后。我认为我们可以安全地假设插入顺序应该保持一致，因为任何引擎都没有必要做其他事情并改变插入顺序。

var obj = {
  "first":"first",
  "2":"2",
  "34":"34",
  "1":"1",
  "second":"second",
  2: "two"
};
// gives result
{ '1': '1',
  '2': 'two',
  '34': '34',
  first: 'first',
  second: 'second' }

Nodejs 属性顺序保证

Nodejs Order of properties guarantee

properties

node.js