NodeJS is a runtime environment that runs on the Chrome V8 engine and parses JavaScript. Its features are event-driven, non-blocking IO, lightweight, efficient, and managed based on npm.
(1) The difference between NodeJS and JavaScript
NodeJS is a runtime environment for running and parsing JavaScript scripts, quite cloud Java to JVM.
（2） NodeJS
① The structure of NodeJS includes V8 JavaScript parsing engine, ECMAScript.
②The middle layer (providing file operations and network operations) is used by developers who are close to the interface of the operating system.
③Hardware layer
(3) NodeJS community
In 2009, hosted to github as a third-party project,
(4) Installation and configuration
Build the windows environment, download the .mis package, and install it in the next step.
(5) Node foundation
①REPL （Read-eval-print-loop）
In fact, it is a cmd command line tool that runs javascript and runs JavaScript code.
(6) global global variable
var a = 123; b = 456;
The difference between these two lines of code is that a global variable var a = 123 of window will be created in the browser parsing js engine; this method will give the a variable to window.
nodejs has a global variable global, which is the same as the browser parsing js to generate a window global object, but the var a variable definition method does not give a to the global gobal, because the scope of nodejs's restriction on js files is within the js file, through a The = value method can give the variable a to the global variable global.
Here are some other commonly used global variables
| __dirname & __filename current folder and current file directory |
| setInterval() & clearInterval() |
| setTimeout() & clearTimeout() |
| console |
| exports & module |
| process |
| require() |
| Class:Buffer |
（7）console
Compared with the console in the browser environment, nodejs is enhanced.
①Assert console.assert(express,out); express is a conditional expression, and out is the content of the output if the expression does not hold
②console.time() & console.timeEnd() Calculate the running time of the two pieces of code, and the parameters passed in should be consistent.
（8）Process
The process object provides the process information of the current node,
| process.version takes the version number and does standard output in the console process.stdout.write(`123123`); process.pid: the process number of the current process. process.version: The version of Node, such as v0.10.18. process.platform: The current system platform, such as Linux. process.env: Points to the environment variable of the current shell, such as process.env.HOME. process.stdout: Points to standard output. process.stdin: Points to standard input. |