The console object

The creation of the global.console object

global.console=new Console(process.stdout,process.seterr);
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Process. stdout: standard output stream object of the current process process.stderr: Standard error stream object of the current process

You can also create your own console object:

const cs =require('console');
const fs=require("fs");
const out =fs.createWriteStream('./appout.log');
const err=fs.createWriteStream('./apperr.log');

const logger=new cs.Console(out,err);
var count=5;
logger.log('count:%d',count);
logger.error('count:%d',count);
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Readline module

The Interface object provided by the readline module can be used to read data line by line from standard input objects or other input stream objects.

const readline=require('readline');
var reader=readline.createInterface({
	input:process.stdin,
  output:process.stdout
});
reader.question('Please enter user name :',(line)=>{
	console.log('The username you entered is: %s... ',line);
  reader.close();// The interpreter will not exit unless it is closed
})
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The Query String module

The Query String module provides operations on the Query String part of the URL.

const queryString=require('querystring');

var qs='ie=utf-8&f=8&rsv_bp=1&srcqid=3605558453180587995'
// Parse the data object from the query string
console.log(querystring.parse(qs));

var data={cid:'sports'.size:'10'.pon:'2'};
// Convert the data object to a query string
console.log(querystring.stringify(data));
console.log(querystring.stringify(data,"#"));// You can specify a separator for each key/value pair. The default is ampersand
console.log(querystring.stringify(data,"#".":"));// The separator between key and value can also be specified as = by default
/ / {
// ie: 'utf-8',
// f: '8',
// rsv_bp: '1',
// srcqid: '3605558453180587995'
/ /}
//cid=%E4%BD%93%E8%82%B2&size=10&pon=2
//cid=%E4%BD%93%E8%82%B2#size=10#pon=2
//cid:%E4%BD%93%E8%82%B2#size:10#pon:2
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The querystring module can only parse part of the querystring, so sometimes you need to use the URL module if you want to parse the full URL.

URL module

The URL module provides operations related to handling different parts of the URL. Contains the following three methods:

const url=require('url');

var requsetUrl='https://www.baidu.com/s?ie=utf-8&f=8&rsv_bp=1&srcqid=3605558453180587995&tn=48020221_20_hao_pg&wd= online flow chart & Oq = Vision %25E8% 25BD%25AF%25E4%25BB%25B6%25E4%25B8%258B%25E8%25BD%25BD&rsv_pq=92df9c4000008d95&rsv_t=1b60taNY6%2BTiridgfP1UaAHne4AOFCHaJ asM1Pf8w7rWdCrjxsUDU1aJYYYtiTW6fb%2FpDC%2F%2F%2FM6V&rqlang=cn&rsv_enter=1&rsv_dl=tb&rsv_sug3=35&rsv_sug1=33&rsv_sug7=100 &bs= Vision software Download '
console.log(url.parse(requsetUrl));// Parse out the components of YRL
console.log(url.parse(requsetUrl,true));// Parse the query string into an object

var urlObj={
  protocol:"http:".slashes:true.auth:"tom:123".port:"8080".hostname:"www.baidu.com".hash:"#section3".query: {pno:"2"},
  pathname:"/news/n1"
};
console.log(url.format(urlObj));

var baseUrl='/project/static/base.html';
console.log(url.resolve(baseUrl,'.. /img/1.jpg'));// Resolve relative urls to base addresses
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DNS module

The DNS module provides bidirectional domain name to IP address resolution. There are three main methods:

const dns=require('dns');
dns.lookup('baidu.com',(err,address,family)=>{
    if (err) throw err;
    console.log("The IP address queried by lookup is :",address);// Resolve a domain name to an IP address
    console.log("Lookup IP address format :IPv",family)
})
dns.resolve('baidu.com',(err,addresses)=>{
    if (err) throw err;
    console.log(addresses);// Resolve a domain name into an array of DNS records
})
dns.reverse('60.221.254.230',(err,hostnames)=>{
    if (err) throw err;
    console.log(hostnames);// Reverse resolve an IP address into a set of domain names
})
//lookup The IP address is 39.156.69.79
The IP address format is IPv 4
/ / / '220.181.38.148', '39.156.69.79'
/ / / '230.254.221.60. Adsl - pool. Sx. Cn']
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Lookup can be implemented without networking, depending on the underlying operating system, and whether the family parameter returns ipv4 or ipv6. Resolve does not depend on underlying operating systems and requires computers to be connected to the Internet. Use the DNS server to search for all IP addresses corresponding to the domain name, including multiple IP addresses. If no IP address is queried, err is returned.

Util module

The Util module provides several utility methods that other Node.js modules and application developers can use.

// Use a format string with a placeholder
var data={name:"Cola".price:2.5.isOnsale:false};
console.log(
    util.format('Name:%s,PRICE:%d,ISONSALE:%s,JSON:%j',
                data.name,data.price,data.isOnsale,data)
)
// Returns a string representation of an object
console.log(util.inspect(data));
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Inheritance between constructors can also be implemented using the Util module

const util=require("util");
const EventRmitter=require('events');

function DBConnection(){
	EventEmitter.call(this);
}
util.inherits(DBConnection,EventEmitter);

var conn=new DBConntion();
console.log(conn instanceof DBConnection);			//true
console.log(conn instanceof EventEmitter);			//true
console.log(DBConnection.super_===EventEmiter);	//true
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