Core Node JS

Console

console object is a global object available in Node JS and Frontend JS. In frontend, console object is used to print data in browser's console window and to debug JS in browser.

console.log

console.log method is used to log output in console.

    console.log("Hello Node");    
    

    var x=2, y=3;
    console.log(x,y);    
    

console.error

console.error method is used to print error messages in console.

    console.error("error found");    
    

Error: error found
    at Object.<anonymous> (/Users/avinash/Desktop/node/src/test.js:26:15)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
    at internal/main/run_main_module.js:17:47       
   

String Substitution

To substitute strings in console, use %s.

    var x=2, y=3;
    console.log("hi %s, how are you?","avi");    
    

Numbers Substitution

To substitute numbers in console, use %d.

    console.log("x is %d and y is  %d.",2,3);    
    

Style console output

To add style to console, use %c and add css properties in second argument.

    console.log("This is %cred","color:red");    
    

    console.log("This is %chighligted text","background:yellow");    
    

Filename

To get file name in node js, we use __filename variable. This variable is available in all files we are working.

Get filename in MacOS

         
    console.log(__filename);
    

Get filename in Window OS

         
    console.log(__filename);
    

Dirname

To get directory name in node js, we use __dirname variable. This variable is also available in all directories we are working.

Get directory name in MacOS

         
    console.log(__dirname);
    

Get directory name in Window OS

         
    console.log(__dirname);
    

Process

process or global.process object is a core module in node js that provide information and control over current nodejs process.

  console.log(process.version);

process is always there in nodejs without using require().

Global

Node JS global object is same like window object in frontend js. Some popular global properties are console, setTimeout, setInterval etc.

         
console.log( console===global.console)// true 
console.log( setTimeout===global.setTimeout)// true 
console.log( setInterval===global.setInterval)// true 
console.log( process===global.process)// true 
  
    

Add property to global

We can also add properties and methods to global object to make it available everywhere in our node application.

         
    global.name="avi";
    console.log(global.name);
    

global using other file

     /* global.js */
global.name="avi";
global.id=212;                          

     /* app.js */
require('./global');
console.log(global.name ) // avi
console.log(global.id ) // 212