①Port occupancy problem:
Running the server today, an error is reported when the node file is enabled, and the terminal prompts: Error: listen EADDRINUSE :::3000
After the query, it is found that two terminals are open, which causes the port to be occupied, and it can be closed.
②Database operation:
To connect to the database, you can use the mongoose module to operate mongodb for additions, deletions, and changes.
③require to load the module
require to load file code, you can load files with .js,.json,.node suffix, and the process is synchronous. so
setTimeout(() => {
module.exports = { a: 'hello' };
}, 0)
require this file to get an empty object {}
④Apply
The application object usually represents an Express application. Create it by calling the top-level express() function exported by the Express module:
var express = require（'express'）;
var app = express （）;
app.get（'/'，function（req，res）{
res.send（'hello world'）;
}）;
app.listen（3000）;
⑤Callback function:
Node convention, if a function requires a callback function as a parameter, the callback function is the last parameter
The first parameter of the callback function itself is the error object passed in in the previous step.
⑥Core module:
http: Provides HTTP server functionality
url: Parse the URL
fs: interact with the file system
querystring: The query string to parse the URL
child_process: create a new child process
util: provides a series of useful gadgets
path: handle file path
crypto: Provides encryption and decryption functions, basically a wrapper around OpenSSL
⑦Exception handling:
Node is a single-threaded runtime environment, once the thrown exception is not caught, it will cause the entire process to crash. Therefore, the exception handling of Node is very important to ensure the stable operation of the system
Generally speaking, Node has three ways to propagate errors:
(1) Use the throw statement to throw an error object, that is, throw an exception
(2) Pass the error object to the callback function, and the callback function is responsible for issuing the error
(3) Issue an error event through the EventEmitter interface