node. JS REPL (Interactive interpreter)

The node. js REPL (Read Eval Print Loop: Interactive interpreter) represents a computer environment, similar to a Window system's terminal (CMD) or unix/linux shell, where we can enter commands in the terminal and receive a response from the system.

Node comes with an interactive interpreter that can perform the following tasks:

• Read -read user input, parse input JavaScript data structure and store in memory.

• execution -execution of input data structures

• Print -Output results

• Loop -loop operation the above steps until the user two times press the ctrl-c button to exit.

Node's interactive interpreter can debug Javascript code very well.

Start learning REPL (take Windows cmd as an example)

We can start Node's terminal by entering the following command:

Node

>

In this case, we can enter a simple expression after > and press ENTER to calculate the result.

Simple expression arithmetic

Next, let's perform a simple math operation in the command-line window of node. js REPL:

Node> 1 +45> 5 / 22.5> 3 * 618> 4 -  13 > 1 + ( 2 * 3 )  -43>     

Using variables

You can store the data in a variable and use it when you need it.

Variable declarations require the use of the var keyword, which is printed directly if the var keyword variable is not used.

Variables that use the var keyword can use Console.log () to output variables.

Node>X= 1010> VarY= 10Undefined> x + y> console.  Log("Hello World")Hello world undefined> console.  Log("www.runoob.com")www.  Runoob.  comundefined               

Multi-line expression

Node REPL supports the input of multi-line expressions, which is a bit like JavaScript. Next, let's perform a do-while loop:

Node> VarX= 0Undefined> Do {...X++;...Console.Log("x:" +X); ...  } while  ( x < 5 x: 1x : 2x:  3x:  4x: 5undefined>         

... The symbol of the three points is automatically generated by the system, you can enter the line after the return. Node automatically detects whether it is a continuous expression.

Underscore (_) variable

You can use the underscore (_) to get the result of the previous expression:

Node> VarX= 10Undefined> var y =20undefined> x + Y30 > var sum = _undefined> Console.log (sum 30undefined>      

REPL command

• Ctrl + C -exits the current terminal.

• Ctrl + C Press two times -Exit Node REPL.

• Ctrl + D -exits Node REPL.

• up/down arrow -View input history commands

• tab -Lists the current command

• . Help-List use commands

• . Break-Exit multi-line expression

• . Clear -Exit multi-line expression

• . Save filename -Saves the current Node REPL session to the specified file

• . Load filename -Loads the contents of the file in the current Node REPL session.

node. JS REPL (Interactive interpreter)