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This article mainly introduces "what is Node.js". In daily operation, I believe many people have doubts about what Node.js is. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful for you to answer the doubts about "what is Node.js?" Next, please follow the editor to study!

Node.js is a JavaScript runtime environment. That sounds good, but what does it mean? How does it work?

The Node runtime environment contains everything you need to execute a JavaScript program.

If you know Java, you will find that they are a bit alike.

JavaScript used to run only in browsers, but Node.js appeared when it was extended to run as a stand-alone program on your computer.

Now you can do more with JavaScript, not just for website interactions and special effects.

JavaScript can now do what other scripting languages such as Python can do.

Both JavaScript and Node.js in your Chrome browser run on the V8 engine. This engine converts your JavaScript code into faster machine code. Machine code is low-level code, and the computer can run it directly without first explaining it.

Why choose Node.js?

This is the official definition given on the official website of Node.js:

Node.js ®is a JavaScript runtime environment built on Chrome's V8 JavaScript engine.

Node.js uses the event-driven non-blocking Istroke O model, which is lightweight and efficient.

Node.js 's package ecosystem npm is an open-source ecosystem in the world.

We have discussed the * * lines of this definition earlier: "Node.js ®is a JavaScript runtime environment built on Chrome's V8 JavaScript engine." Now let's understand the remaining two lines so we can figure out why Node.js is so popular.

I take O means input / output. It can be anything from reading / writing to a local file to sending a HTTP to API.

IPot O takes time, so it blocks other functions.

To consider this situation, we need to request the back-end database to get the details of user1 and user2, and then print them on the screen or console. The response to the request takes time, but two requests for user data can be executed independently at the same time.

Blocking Ipicuro (left) and non-blocking Iripple O (right)

Blocking IPUBO

In the blocking method, a data request for user1 is not initiated until user2's data is output to the screen.

If this is a Web server, we must start a new thread for each new user. But JavaScript is single-threaded (it's not really true, but it has a single-threaded event loop, which we'll discuss later). So this makes JavaScript less suitable for multithreaded tasks.

This is a non-blocking opportunity to use your talents.

Non-blocking IPUBO

On the other hand, if you use a non-blocking request, you can initiate a data request for user2 without waiting for a response to the user1 request. You can start the two requests in parallel.

This non-blocking Ithreading eliminates the need for multithreading because the server can handle multiple requests at the same time.

JavaScript event loop

The following is a brief step-by-step description of how the JavaScript event loop works.

Feed main () into the call stack.

Feed console.log () into the call stack. Then run it immediately and pop up.

The setTimeout (2000) is fed into the stack. SetTimeout (2000) is a Node API. When calling it, register the event callback first. The event waits for 2000 milliseconds before calling back the function.

After registering in API, setTimeout (2000) pops up from the call stack.

Now the second setTimeout (0) is registered in the same way. We now have two Node API waiting to be executed.

After waiting for 0 seconds, setTimeout (0) is moved to the callback queue, and the same thing happens to setTimeout (2000).

In the callback queue, the function waits for the call stack to be empty because each statement is executed once. This is handled by the event loop.

* A console.log () runs and main () pops up from the call stack.

If the event loop detects that the call stack is empty and the callback queue is not empty. It moves the callback (in first-in-first-out order) to the call stack and executes.

Npm

These are libraries built by an awesome community that can solve most of your general problems. There are many packages in npm (Node package manager) that can be used in your program to make your development faster and more efficient.

Require

Require does three things:

It loads modules bundled with Node.js, such as file systems and HTTP, from Node.js API.

It loads third-party libraries installed from npm, such as Express and Mongoose.

It allows you to require your own files and modularize the project.

Require is a function that takes the parameter "path" and returns module.exports.

Node module

The Node module is a reusable code block, and its existence does not unexpectedly affect other code.

You can write your own module and use it in various programs. Node.js has a set of built-in modules that can be used without further installation.

V8 accelerates JavaScript by using C++

V8 is an open source runtime engine written in C++.

JavaScript = > V8 (C + +) = > Machine Code

V8 implements a script named ECMAScript specified in ECMA-262. ECMAScript is created by Ecma International and is used to standardize JavaScript.

V8 can be run independently or embedded in any C++ program. It has hooks that allow you to write your own C++ code for JavaScript to use.

This actually allows you to add functionality to JavaScript by embedding V8 into C++ code so that your C++ code implements more functionality than the ECMAScript standard.

As Greg Bulmash caught my attention, in addition to V8, there are many different JavaScript engines, such as Mozilla's SpiderMonkey, Microsoft's Chakra and so on. More things can be found here.

Event

Events mean that we can respond to what happens in the program. There are two types of events in Node.

System event: from a kernel based on the libuv library implemented in C++. (for example, after reading the file).

Custom event: JavaScript core.

Write a Hello World in Node.js

Create the file app.js and add the following to it.

Console.log ("Hello World!")

Open the terminal, change the directory to the folder where you saved the file, and then run node app.js.

It's as simple as that. The "Hello World" you wrote in Node.js is running.

At this point, the study of "what is Node.js" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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