javascript node.js next() [英] javascript node.js next()
问题描述
我在node.js中看到很多使用 next
。
I see a lot of use next
in node.js.
这是什么,它在哪里来自?它有什么作用?我可以在客户端使用吗?
What is it, where does it come from? What does it do? Can I use it client side?
很抱歉,例如这里使用它:
http://dailyjs.com/2010/12/06/node-tutorial-5/
Sorry it's used for example here: http://dailyjs.com/2010/12/06/node-tutorial-5/
看对于loadUser函数。
look for the loadUser function.
推荐答案
这似乎是Node.js控制流代码中的变量命名约定,其中有一个引用下一个要执行的函数被赋予一个回调函数,以便在它完成时启动它。
This appears to be a variable naming convention in Node.js control-flow code, where a reference to the next function to execute is given to a callback for it to kick-off when it's done.
例如,请参阅此处的代码示例:
See, for example, the code samples here:
- http://blog.mixu.net/2011/02/02/essential-node-js-patterns-and-snippets/
让我们来看看你发布的例子:
Let's look at the example you posted:
function loadUser(req, res, next) {
if (req.session.user_id) {
User.findById(req.session.user_id, function(user) {
if (user) {
req.currentUser = user;
return next();
} else {
res.redirect('/sessions/new');
}
});
} else {
res.redirect('/sessions/new');
}
}
app.get('/documents.:format?', loadUser, function(req, res) {
// ...
});
loadUser
函数需要一个函数第三个参数,绑定到名称 next
。这是一个正常的函数参数。它包含对下一个要执行的操作的引用,并在完成 loadUser
后调用(除非找不到用户)。
The loadUser
function expects a function in its third argument, which is bound to the name next
. This is a normal function parameter. It holds a reference to the next action to perform and is called once loadUser
is done (unless a user could not be found).
在这个例子中,名称 next
没有什么特别之处;我们可以把它命名为任何东西。
There's nothing special about the name next
in this example; we could have named it anything.
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