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Command Line Javascript: Javascript Explained

Table of Contents

Command line Javascript or CLI Javascript is the ability to write and execute code within a terminal, or command line. This way of programming involves writing code in order to execute specific commands, as opposed to running it in a web browser. Each command can create a process which typically contains pre-programmed functions and variables. While many people think of Javascript as a web development language, CLI Javascript is gaining in popularity as a powerful tool for other applications, such as automation and system administration tasks.

What is Command Line Javascript?

CLI Javascript is a quick and simple way to write code within a terminal. It is a variant of internet scripting language, Javascript, that is designed to be used in a command line environment. Unlike the code written for web browsers, the code you write for command line applications is not visible on the page. The Javascript written in the terminal, or command line, compiles commands to run programs and automate tasks without the need for manual execution.

CLI Javascript can be used as a scripting language to write programs, utilities and bind together pieces of software. It can also be used for systems administration and automation tasks. For example, automating repetitive processes, downloading files from a web server, or writing scripts to launch an application.

CLI Javascript is a powerful tool for developers, as it allows them to quickly and easily create scripts and programs that can be used to automate tasks and processes. It is also a great way to learn the basics of programming, as it is easy to understand and use. With CLI Javascript, developers can create powerful applications and scripts that can be used to automate tasks and processes, making them more efficient and productive.

Benefits of Command Line Javascript

Command Line Javascript has many advantages over other programming languages. It has a very low learning curve, so developers can get started quickly without having to learn all of the complicated syntax associated with other languages. Its simple syntax makes it easy to read and understand and it has the ability to quickly, efficiently, and accurately execute commands.

In addition to its ease of use, CLJS is also very powerful. It can be used to programmatically interact with applications and systems that provide APIs and it can be used to quickly automate simple or complex tasks. It can also provide access to system-level functions, allowing developers to write powerful scripts that can manipulate processes and change system configurations.

How to Use Command Line Javascript

Using command line JavaScript is relatively simple. All you have to do is create a file with a JavaScript extension (e.g “myfile.js”) and write the code within it. Once the code is written, you can run it from the command line using Node.js and the command ‘node myfile.js’. With Node.js installed, you can then run CLI JavaScript by simply typing ‘node scriptname.js’ into your terminal.

Working with Variables and Expressions

Variables are an important part of any programming language – they are used to store data which can be accessed later. Command Line Javascript makes use of variables in much the same way as regular Javascript does. Variables are declared using the ‘var’ keyword followed by your choice of name for the variable. Thus, a basic declaration might look something like this: var myvariable = 0.

In addition to variables, CLI JavaScript also makes use of expressions which are used to perform calculations on values that are stored in variables. Expressions make use of operators such as addition (‘+’) or subtraction (‘-‘) which are used to specify what operations should be performed on the variable values they are given.

Working with Arrays and Objects

Arrays and objects are both data structures that are widely used in programming. Arrays are ordered lists of values that can store any type of data, such as numbers or strings, while objects are unordered sets of key-value pairs which also store any type of data.

In CLI JavaScript, both arrays and objects can be created using the ‘var’ keyword. To create an array, use the square brackets ‘[]’ followed by the values that should be contained within it. For example, var myarray = [1,2,3]. To create an object, use the curly braces ‘{}’ followed by the key-value pairs that make up the object. For example var myobject = {name: ‘Bob’, age: 25}.

Working with Functions and Control Flow Structures

Functions are blocks of code that are designed to perform specific tasks. In CLI JavaScript, function can be defined using the keyword ‘function’ followed by the parameters that will be used by the function (e.g function myFunction(parameter1){…).Once defined, functions can be used within the scope of their definition, or called from outside of their scope using their name.

In addition to functions, control flow structures are also used in command line JavaScript. Control flow structures allow developers to create dynamic programs that respond based on different situations and conditions. Some of the common structures used in CLI JavaScript include ‘if/else’, ‘while’, and ‘for’ statements.

Working with Regular Expressions

Regular expressions are very useful when it comes to processing strings in command line applications. They allow developers to search for patterns within strings or check if strings match a certain pattern or criteria. Regular expressions need to be written in a specific format in order for them to be understood by the computer and processed correctly.

Regular expressions typically consist of two parts: the text that you want to match on (the ‘pattern’), and any flags (e.g i for case-insensitive) that should be applied when searching for matches. For example, /php/i would match ‘PHP’. Regular expressions can be used with both strings and objects in CLI applications.

Commonly Used Command Line Tools

There are many different command-line tools available for use when developing command line applications. Some of these tools include Node.js, NPM, Grunt, Gulp, and Bash. These tools each provide their own set of features and capabilities which can come in handy when developing command line applications.

Node.js allows developers to write server-side applications using JavaScript and is often used for creating CLIs. NPM is a package manager for Node which can be used to install third-party packages and libraries. Grunt and Gulp are task runners which allow developers to quickly automate tasks such as minification, linting and compiling code.

Tips for Writing Effective Code

Writing effective command line code can be tricky due to its relatively small scope and lack of visual aids when working with data. Here are some tips you should keep in mind when writing your own CLI applications:

  • Write self-documenting code: Make sure your code is well-documented so that other people will be able understand what’s going on.
  • Avoid coding by numbers: Instead of simply writing commands without thought, think about how your code could be improved or optimized for better performance.
  • Test your code frequently: Test your code frequently as you write it in order to ensure everything works correctly.
  • Keep your code concise: Try to keep your code concise so that it’s easier to read and understand.
  • Remember security: Keep security in mind when writing code so that your apps don’t become vulnerable.


Command Line Javascript (CLI Javascript) is a powerful programming language that can be used for automation and system administration tasks. It has an easy-to-learn syntax and can be used with many different tools, such as Node.js or NPM. When writing your own command line applications, remember to keep your code well-documented, avoid coding by numbers and test your code frequently in order to produce effective results.

Nisha Kumari

Nisha Kumari

Nisha Kumari, a Founding Engineer at Bito, brings a comprehensive background in software engineering, specializing in Java/J2EE, PHP, HTML, CSS, JavaScript, and web development. Her career highlights include significant roles at Accenture, where she led end-to-end project deliveries and application maintenance, and at PubMatic, where she honed her skills in online advertising and optimization. Nisha's expertise spans across SAP HANA development, project management, and technical specification, making her a versatile and skilled contributor to the tech industry.

Written by developers for developers

This article was handcrafted with by the Bito team.

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