在socket.io中表达express的目的是什么？

Question

I apologize for this novice question, what is the purpose of express in socket.io and why we need to require express in creating chat application?.can we just use socket.io API to create chat application ?

Thank you in advance.

Answer 1

Express is an micro-framework for creating Web Applications with Node.js. You could think of it as a "Ruby on Rails" extremely lightweight alternative.

You use it with Socket.io because you normally need a base for starting creating an web app. Express is usually the common choice, but there are others like Sails.js. You could use plain Node.js API to create an application with Socket.io too.

Answer 2

A webSocket connection is initiated with an http connection that contains special webSocket headers that is then "upgraded" from http to the webSocket protocol when both sides agree to move to webSocket. Thus, you need a listening http server in nodejs in order to field webSocket connections.

You don't have to use Express for your web server to use with incoming webSocket connections (you can use just the plain http module in nodejs if you want or anything else that listens for incoming http connections), but socket.io has direct integration with Express such that it takes only a single line of code for socket.io to hook into Express and then be listening for incoming webSocket connections.

And, as others have said, whenever you have a webServer, you often are also serving web pages and Express is an easy and popular way to server web pages via nodejs so many people using socket.io are already using Express too.