004 Node.js REPL Terminal

REPL Terminal
Node.js have virtual environment called REPL or Node Shell ,REPL stands for Read Eval Print Loop.REPL is commonly used for debug JS code.

• Read − Reads user's input, parses the input into JavaScript data-structure, and save in memory.

• Eval − Evaluates the data structure.

• Print − Prints the result.

• Loop − Loops the above command until the user presses ctrl-c twice.

To open REPL , Open command prompt , then type "node".Below is the image

You can evaluate expression in REPL also.


Example 1 (Simple Expression)
10+20
=30

Output

Example 2 (Complex Expression)
12+((11+3)*9)/3
=54


Output

Variable in REPL 

 
Variables are used to store values. var keyword is used for variable declaration.You can evaluate expression with variable also.


Example 1 (Simple Expression)
> var a=10
undefined
> var b=20
undefined
> a+b
30Output :

Multiline Expression  

Node.js REPL supports multiline expression similar to JavaScript.

Example 1 

for(var l=0;l<20 br="" l=""> <20 20="" l="">

<20 br="" l="">{
  console.log(l*l);
}

Output :

 

 

Node.js Underscore Variable 

You can also use underscore _ to get the last evaluated value.

Example 1 

> 1+9+8+6
24
> _
24

Output :

 

 

REPL Commands

help:The .help command is used to display all the  REPL commands.

Example

C:\Users\dbhattacharjee>node
> .help

Output :

exit :Exit the repl

Example 
C:\Users\dbhattacharjee>node
> .exit 

Output :
C:\Users\dbhattacharjee>



save :Save all evaluated commands in this REPL session to a file.

Example
C:\Users\dbhattacharjee>node
> 5+9+3
17
> .save myData.txt
Session saved to:myData.txt



load :Load JS from a file into the REPL session

Example 



C:\Users\dbhattacharjee>node
> 4+5+6+4
19
> .save myFile.txt
Session saved to:myFile.txt
> .load myFile.txt
4+5+6+4

19
>

editor : Enter editor mode
 
Example
C:\Users\dbhattacharjee>node
> .editor
// Entering editor mode (^D to finish, ^C to cancel)
console.log('hello world');
hello world
undefined
>

tab keys :list of current commands.
Example

 REPL Keyboard Commands

(a) ctrl + c :It is used to terminate the current command.
(b) ctrl + c twice :It terminates the node repl.
(c) ctrl + d :It terminates the node repl.
(d) up/down keys :It is used to see command history and modify previous commands.