REPL is one of the Nodejs feature. It is an interactive program environment. REPL stands for Read Eval Print Loop. Using REPL, we can able to do simple arithmetic calculations. In REPL environment, an user can enters one and more expressions, which are evaluated and the result displayed.
The following are the components of REPL
- Read - Accepts input from the user and parses.
- Eval - Takes data structure and evaluates.
- Print - Prints the result.
- Loop - Runs commands until termination.
Nodejs REPL- Start
To start the REPL environment, run the following command
$ node
It will open the REPL environment with the symbol `>`
REPL - Variable
Following are sample variable usage codes
$ node
> a = 1
1
> var b = 2
undefined
> a + b
3
> var sum = _
undefined
> console.log(sum)
3
undefined
>
If you use `var` keyword, it wont print the value. it will only store the value. You can use underscore `_` to get the last result.
REPL - Expression & Loop
Following are sample expression codes
$ node
> 1 + 2
3
> 2 + ( 3 * 4 )
14
>var ind = 0
undefined
> do {
... ind++;
... console.log("ind: " + ind);
... } while ( ind < 3 );
ind: 1
ind: 2
ind: 3
undefined
Some REPL Commands
- ctrl + c − Terminates current command.
- ctrl + c twice − Terminates REPL.
- ctrl + d − Terminates REPL.
- Up/Down Keys − For command history.
- tab Keys − Lists current commands.
- .help − Lists all commands.
