javascript - 如何使 `Object.keys` 遵守对象中键为 'declared' 的顺序？

Question

给定对象:

var opts = {
    'all': 'All',
    0: 'Some option',
    1: 'Cookies',
};

Object.keys(opts) 返回:

["0", "1", "all"]

当我期待这个:

["all", "0", "1"] // The order in which the keys are 'declared' in the obj

---

如何按照属性在对象中出现的顺序遍历属性？

谢谢。

Answer 1

ECMA-262, section 12.6.4关于 for-in 语句:

The mechanics and order of enumerating the properties (step 6.a in the first algorithm, step 7.a in the second) is not specified.

你可以改用数组:

var opts = [
    {key: 'all', value: 'All'},
    {key: 0,     value: 'Some option'},
    {key: 1,     value: 'Cookies'}
];

或者，在 ES6 中，Map对象:

var opts = new Map([
    ['all', 'All'],
    [0,     'Some option'],
    [1,     'Cookies']
]);

opts.forEach(function(val, key) {
    console.log(key, val);
});

在这种情况下，forEach 将始终按插入顺序迭代键值对。