The article directories

• 2.1. Install the Node environment · Check the version of the current Node environment
• 2.2. Hello World
• • • Case 1: Create a file named 00-helloworld.js and write
    • Case 2: No DOM and BOM
    • Case 3: Reading a file
    • Case 4: Write a document
    • Case 5: Reading a file that does not exist
    • Plus misjudgment
    • Failed to write file
    • File writing succeeded

2.1. Install the Node environment · Check the version of the current Node environment

• Download: nodejs.org/en/download…

• The installation

  • Fool’s waynextIt is ok
  • For those that have already been installed, reinstalling will upgrade

• Check whether the Node environment is installed successfully

Node -v or node --versionCopy the code

• The environment variable

2.2. Hello World

Case 1: Create a file named 00-helloworld.js and write

var foo = 'hello nodejs'

console.log(foo)
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• incmdWindow output orgitbashOr vscode’s own terminal

node 00-helloworld.js
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Case 2: No DOM and BOM

console.log(window)
console.log(document)
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Case 3: Reading a file

• JavaScript in browsers does not have file-manipulation capabilities
• But JavaScript in Node has file-manipulation capabilities
• Fs isfile-systemFile system is short for file system
• If you want to perform file operations in Node, you must importfsThis core module
• infsIn this core module, all the relevant file operations are providedAPI
• Such as:fs.readFileIt’s used to read files

1. Load the FS core module using the require method

var fs = require('fs')
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2. Read the file

   • The first parameter is the path to the file to read

   • The second argument is a callback function

     • successful

       • The data of data
       • error null

     • failure

       • Data undefined Has no data
       • Error Error object

• error
  
  If the read fails,errorThat’s the error object
  
  If the read succeeds,errorisnull
• data
  
  If the read succeeds,dataThat’s the data that you read
  
  If the read fails,errorThat’s the error object

fs.readFile('./data/hello.txt'.function (error, data) {
	console.log(data)
})
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• In the newhello.txtWrite to file

Hello nodejs hello Node.jsCopy the code

• performNode 02- Reads files

var fs = require('fs')
fs.readFile('./data/hello.txt'.function (error, data) {
	console.log(data)
})
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<Buffer 68 65 6c 6c 6f 20 6e 6f 64 65 6a 73 0d 0a 0d 0a>
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• The files are actually storing binary data, 0, 1
• Why don’t we see zeros and ones here? The reason is binary has been converted to hexadecimal
• But neither binary 01 nor hexadecimal is known to humans
• So we can go throughtoStringMethod to convert it to a character we can recognize

var fs = require('fs')
fs.readFile('./data/hello.txt'.function (error, data) {
	console.log(data.toString())
})
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• performNode 02- Reads files

Case 4: Write a document

var fs = require('fs')

fs.writeFile('. / data/hello. Md '.'Hi, I'd like to introduce you, I'm Node.js'.function (error) {
  console.log('File write succeeded')})Copy the code

Case 5: Reading a file that does not exist

• a.txtHas not been created

var fs = require('fs')
fs.readFile('./data/a.txt'.function (error, data) {})Copy the code

• No prompt is displayed after execution

• Already createdhello.txtTo check for errors

var fs = require('fs')
fs.readFile('./data/hello.txt'.function (error, data) {
	console.log(error)
})
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• If yes, the data is successfully read

• Make it nonexistenta.txt

var fs = require('fs')
fs.readFile('./data/a.txt'.function (error, data) {
	console.log(error)
})
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• If the command is executed, the read fails

Error is an error object, and data is real data

var fs = require('fs')
fs.readFile('./data/a.txt'.function (error, data) {
	console.log(error)
	console.log(data)

	console.log(data.toString())
})
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Undefined has no toString attribute

• successful

  • The data of data
  • error null

• failure

  • Data undefined Has no data
  • Error Error object

Plus misjudgment

var fs = require('fs')
fs.readFile('./data/a.txt'.function (error, data) {
	 if (error) {
    console.log('File reading failed')
    // return
  		} else {
    console.log(data.toString())
  	}
})
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Failed to write file

• Now the file name is? .txtBecause special characters cannot be used as file names in Windows

var fs = require('fs')
fs.writeFile('./data/? .txt'.'Hi, I'd like to introduce you, I'm Node.js'.function (error) {
   console.log(error)   // Check for errors
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File writing succeeded

var fs = require('fs')
fs.writeFile('. / data/hello. TXT '.'Hi, I'd like to introduce you, I'm Node.js'.function (error) {
   console.log(error)   // Check for errors
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var fs = require('fs')
fs.writeFile('. / data/hello. TXT '.'Hi, I'd like to introduce you, I'm Node.js'.function (error) {

   if (error) {
    console.log('Write failed')}else {
    console.log('Write succeeded')}Copy the code