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Node.js REPL


The term REPL stands for Read Eval Print and Loop. It specifies a computer environment like a window console or a Unix/Linux shell where you can enter the commands and the system responds with an output in an interactive mode.

REPL Environment

The Node.js or node come bundled with REPL environment. Each part of the REPL environment has a specific work.

Read: It reads user’s input; parse the input into JavaScript data-structure and stores in memory.

Eval: It takes and evaluates the data structure.

Print: It prints the result.

Loop: It loops the above command until user press ctrl-c twice.

How to start REPL

You can start REPL by simply running “node” on the command prompt. See this:

nodejs-repl1

You can execute various mathematical operations on REPL Node.js command prompt:

Node.js Simple expressions

After starting REPL node command prompt put any mathematical expression:

  1. Example: >10+20-5
  2. 25

nodejs-repl2

  1. Example2: >10+12 + (5*4)/7

nodejs-repl3

Using variable

Variables are used to store values and print later. If you don’t use var keyword then value is stored in the variable and printed whereas if var keyword is used then value is stored but not printed. You can print variables using console.log().

Example:

nodejs-repl4

Node.js Multiline expressions

Node REPL supports multiline expressions like JavaScript. See the following do-while loop example:

  1. var x = 0
  2. undefined
  3. > do {
  4. … x++;
  5. … console.log(“x: ” + x);
  6. … } while ( x < 10 );

nodejs-repl5

Node.js Underscore Variable

You can also use underscore _ to get the last result.

Example:

nodejs-repl6

Node.js REPL Commands

Commands Description
ctrl + c It is used to terminate the current command.
ctrl + c twice It terminates the node repl.
ctrl + d It terminates the node repl.
up/down keys It is used to see command history and modify previous commands.
tab keys It specifies the list of current command.
.help It specifies the list of all commands.
.break It is used to exit from multi-line expressions.
.clear It is used to exit from multi-line expressions.
.save filename It saves current node repl session to a file.
.load filename It is used to load file content in current node repl session.

Node.js Exit REPL

Use ctrl + c command twice to come out of Node.js REPL.

nodejs-repl7

 

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