javascript - 比较数组内的 id 和 NodeJS 的 id 时出现无法理解的结果

Question

我想要返回结果 true，但是 javascript 说它是 false。有人可以解释一下为什么吗？这是 console.log 的日志

5a8f1df35f65a820f4dc56ed 5a8db5d449c0572dbc60548c

false

5a91e3de5b8d6d18580c9aff 5a8db5d449c0572dbc60548c

false

5a91e3f45b8d6d18580c9b00 5a8db5d449c0572dbc60548c

false

5a8db5d449c0572dbc60548c 5a8db5d449c0572dbc60548c

.get('/selected/board', function (req, res) {
    var isExist = false;

    Board.findById({ _id: req.query._id })
        .then((board) => {
            board.users.forEach(element => {
                console.log(element == req.user._id)
                console.log(element, req.user._id) 
            });  
            // res.json(board);
        })
        .catch((err) => {
            res.status(404).json('Cant download.')
        })
})

编辑

element: "5a8f1df35f65a820f4dc56ed" req.user._id: "5a8db5d449c0572dbc60548c"

false

element: "5a91e3de5b8d6d18580c9aff" req.user._id: "5a8db5d449c0572dbc60548c"

false

element: "5a91e3f45b8d6d18580c9b00" req.user._id: "5a8db5d449c0572dbc60548c"

false

element: "5a8db5d449c0572dbc60548c" req.user._id: "5a8db5d449c0572dbc60548c"

true

element: "5a8f1df35f65a820f4dc56ed" req.user._id: "5a8db5d449c0572dbc60548c"

false

element: "5a91e3de5b8d6d18580c9aff" req.user._id: "5a8db5d449c0572dbc60548c"

false

element: "5a91e3f45b8d6d18580c9b00" req.user._id: "5a8db5d449c0572dbc60548c"

false

element: "5a8db5d449c0572dbc60548c" req.user._id: "5a8db5d449c0572dbc60548c"

true

Answer 1

board.users 中的元素有一个属性 id，其类型为 ObjectId("45465456464")，因此您进行的比较执行遵循以下规则:

            +--- Operand ObjectId(...)
            |
            v
ToPrimitive(element) == B  <---- String from the request.

因此，这个条件始终为假

element == req.user._id

看看这个文档 Loose equality using ==

另一种方法是转换为字符串

element.toString() == req.user._id