JavaScript is an interpreted language. This means that it is executed directly by the interpreter rather than being compiled into machine code that the computer’s hardware can execute. This behavior also makes it a flexible and dynamic language, but it can also be slower than compiled languages.

This tutorial will demonstrate whether JavaScript is a compiled or interpreted language.

Is JavaScript Compiled or an Interpreted Language?

First of all, let’s understand the working of an interpreter and compiler and how the script will be interpreted in a browser.

Compiled or an Interpreted Language

The “compilation” is the process of transforming the source code of a program into machine-readable binary code prior to execution. This improves application performance since the compiler optimizes the code for the platform of the end user. An “Interpreter” executes the program instructions without forcing them to be precompiled into a machine-readable format.

Advantages

Compiled Languages	Interpreted Languages
Compiled languages are generally faster than interpreted languages because the code is compiled into machine code, which the computer’s processor can directly execute.	Interpreted languages generally have a faster development time because the code does not need to be compiled before it can be executed.
Compilers can detect and report errors during the compilation process, making it easier to find and fix bugs in the code.	Interpreted programs do not need to be compiled for specific platforms, meaning they can be run on any system with an interpreter installed.
Compiled languages are secure because the compiled code is translated into machine-understandable code/binary code.	Interpreted languages are more flexible as it allows them to modify the code at runtime, which makes it easier to experiment with different approaches and make changes to the code quickly.
They use fewer resources than interpreted programs.	Interpreted languages are well-suited for interactive environments, such as a command-line interface or a web browser, because they allow for code to be executed incrementally. This makes it easy to test small pieces of code or interactively debug programs.

Disadvantages

Compiled Languages	Interpreted Languages
Extra time is required to complete the compilation stage completely before testing.	They often report errors at runtime, which can be more difficult to debug.
Platform dependent on the resulting binary code.	As the interpreted languages are easier to modify at runtime, they are less secure and are more vulnerable to reverse engineering.
Compiled languages are generally less flexible because they do not allow code to be modified at runtime.	They typically use more resources than compiled programs because they require an interpreter to operate.
They are not well-suited for interactive environments, such as a command-line interface or a web browser, because they do not allow incremental code to be executed.	Interpreted languages are generally unsuitable for high-performance, resource-intensive applications, such as operating systems or databases, because of their slower performance and reduced security.

How is Script Interpreted in a Browser?

Every browser has its engine, and varied implementation, which is excellent for the competition and means increased productivity. These engines run the scripts. When the script is loaded in the browser, the interpreted languages engine converts it line by line to machine code and executes it. A feature of the browser’s engine run-time interpreter is the JIT (Java-in-time) compilation, which allows methods to be called by compiling bytecode into the machine code instructions of the currently operating machine rather than by interpreting it every time.

Is JavaScript Compiled or an Interpreted Language?

JavaScript is an interpreted language but acts as a compiled language because of JIT. JIT (Just-in-time) compilation is a technique utilized to improve/enhance the productivity of interpreted languages. In a JIT-based interpreter, the interpreter compiles the program’s source code into machine code at runtime rather than interpreting it directly. JIT compilation can be an effective way to achieve the benefits of both compiled and interpreted languages.

JavaScript can operate in an interpreted manner in older browsers. JavaScript code is always compiled because every browser currently supports “JIT”. We believe that the environment in which JavaScript is run determines whether it is a compiled or an interpreted language. If it runs in old browsers, it is interpreted, while if it runs in modern browsers, it is compiled.

Conclusion

JavaScript is an interpreted language, but it acts as a compiled language because of JIT. JavaScript code is always compiled because every browser currently supports “JIT”. The environment in which JavaScript is run determines whether it is a compiled or an interpreted language. This tutorial demonstrated whether JavaScript is a compiled or interpreted language.