小编Dum*_*uma的帖子

当我使用在nodejs中的"$ where"子句中传递的函数查询我的数据库时,它总是返回db中的所有文档.

例如,如果我这样做

var stream = timetables.find({$where: function() { return false; }}).stream();

它将所有文件归还给我.相反,如果我这样做

var stream = timetables.find({$where: 'function() { return false; }'}).stream();

该函数实际执行,此代码不返回任何文档.

问题是,如果我在字符串my function中转换上下文的绑定被删除,我需要它们来进行更复杂的查询.例如:

var n = 1;
var f = function() { return this.number == n; }
var stream = timetables.find({$where: f.toString()}).stream();
// error: n is not defined

这是正常行为吗？我怎样才能解决我的问题？请原谅我英语不好!

In a React functional component with the useState hook I don't know how to run multiple async operations without having conflict on the final result.

If the initial state is an object and every async operation performs a change on a given key, it's possible to use the spread operator in order to set a new state. Example:

const [oldState, setNewState] = React.useState({ /* something */ });
const asyncOperation = async () => {
   await somethingAsync();
   setNewState({
      ...oldState,
      key: 'newValue', …