node. JS--There is a Param method in the router module

This time has been looking at the express framework of the API, recently saw router, the following is what I think need to be aware of the place:

Router module has a Param method, just start to look a little vague, the official website is probably described as follows:

1	Map logic to route parameters.

It probably means that the mapping logic of the route parameter

This may be 1:30 and will not understand the function, especially do not know the order of Get and Param execution

Then look at the source of the introduction:

123	Map the given param placeholder `name`(s) to the given callback.Parameter mapping is used to provide pre-conditions to routeswhich use normalized placeholders

This is much clearer, translation comes to say:

Make a mapping between the given parameter and the callback function as a precondition for routing using the normalized placeholder.

A specific code is given below:

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varexpress = require(‘express‘);varapp = express();varrouter = express.Router();router.count = 0;router.get(‘/users/:user‘, function(req, res, next) {    router.count ++;    console.log(router.count);});router.param(‘user‘, function(req, res, next, id) {    router.count ++;    res.send({count: router.count});    next();});app.use(router);app.listen(3000);

Command Line Input

Node Xxx.js

Browser access

Http://localhost:3000/users/bsn

This time the command line outputs 2, and the browser outputs

{Count:1}

Therefore, the Param is executed before the get

node. JS--There is a Param method in the router module