The REPL provides shortcuts to decrease coding time when possible. The REPL also includes some handy shortcuts to make that process easier.
#Nodejs repl code
You can use the REPL to try out bits of JavaScript code before including them into your programs. prompt is now gone and the > prompt returns: undefined Pressing ENTER after the closing curly bracket will display an undefined, which is the “return value” of the function assignment to a variable. To make it easier to read, the REPL adds 3 dots and a space on the next line, so the following code appears to be indented.Įnter the second and third lines of the function, one at a time, pressing ENTER after each: return num + 3 The REPL noticed an open curly bracket and therefore assumes you’re writing more than one line of code, which needs to be indented. Then, pressing ENTER will change the prompt to. Start the function by typing the following: For example, you can create a function that adds 3 to a given number. Multi-line blocks of code are supported as well. By default, any returned value will appear on the screen. Type the following at the prompt and press ENTER:īecause the REPL returns values, you don’t need to use console.log or similar functions to see the output on the screen. For example, you can multiply age by two. The age variable will be available until you exit the REPL session. Like before, with console.log, the return value of this command is undefined. Creating a variable in the REPL works in the same fashion as working with. Rarely do you just work with literals in JavaScript. The undefined is the return value of the function. Because console.log prints a string instead of returning a string, the message is seen without quotes. The first result is the output from console.log, which prints a message to the stdout stream (the screen). Pressing ENTER yields the following output: Hi When writing Node.js code, it’s common to print messages via the global console.log method or a similar function. If the string you entered used a single quote, the REPL is smart enough to use double quotes in the output. In JavaScript, the quotes used for a string do not affect its value. Note: You may have noticed that the output used single quotes instead of double quotes. Concatenate the following strings in your REPL by typing:Īgain, press ENTER, and the string expression is evaluated: 'Hello World'
The REPL can also process operations on strings. Press ENTER, and the output will be 2, as expected: 2 In the previous step you already tried out addition of two numbers, now let’s try division. Almost every valid JavaScript or Node.js expression can be executed in the REPL.
The REPL is a quick way to test JavaScript code without having to create a file. Step 2 - Executing Code in the Node.js REPL
With starting and stopping out of the way, let’s take a look at how you can use the REPL to execute simple JavaScript code. exit, or press CTRL+D once, or press CTRL+C twice, which will return you to the shell prompt. When you press ENTER, the REPL will evaluate the expression and return: 4 The > symbol lets you know that you can enter JavaScript code to be immediately evaluated.įor an example, try adding two numbers in the REPL by typing this: To start it, simply enter node in your command line shell: If you have node installed, then you also have the Node.js REPL.
#Nodejs repl how to
A basic knowledge of JavaScript, which you can find here: How To Code in JavaScript.
#Nodejs repl install
To install this on macOS or Ubuntu 18.04, follow the steps in How to Install Node.js and Create a Local Development Environment on macOS or the “Installing Using a PPA” section of How To Install Node.js on Ubuntu 18.04.
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