Is JavaScript a Compiled or Interpreted Language?

When it comes to programming languages, there are two types of languages: compiled and interpreted. JavaScript is often referred to as an interpreted language, but this is not entirely accurate. To answer the question, let’s first define what compiled and interpreted languages are.

Compiled vs Interpreted Languages

Compiled languages are those in which the source code is transformed into machine code at compile time. This means that the code is translated into machine-readable code before it is executed. Examples of compiled languages include C, C++, Java, and Go.

On the other hand, interpreted languages are those in which the source code is executed directly without being compiled first. The code is read line by line and executed at runtime. Examples of interpreted languages include Python, Ruby, and JavaScript.

JavaScript as an Interpreted Language

JavaScript is often referred to as an interpreted language because it is executed line by line at runtime. However, this is not entirely true. JavaScript is actually a Just-In-Time (JIT) compiled language. This means that the code is compiled at runtime, but only the parts of the code that are actually executed are compiled.

The JavaScript engine in a browser, such as Google Chrome’s V8 engine, uses a JIT compiler to optimize the code for execution. When the code is first loaded, it is parsed and compiled into bytecode. Then, as the code is executed, the JIT compiler optimizes the code by recompiling it into machine code. This allows JavaScript to be executed much faster than traditional interpreted languages.

Example

Let’s look at an example to illustrate how JavaScript is compiled and executed at runtime:

function add(a, b) {
  return a + b;
}

let result = add(2, 3);
console.log(result);

When this code is executed, the following steps occur:

1. The code is parsed and compiled into bytecode.
2. The function add is defined in memory.
3. The function is called with the arguments 2 and 3.
4. The JIT compiler optimizes the code for execution.
5. The optimized code is executed and the result is logged to the console.

Conclusion

In conclusion, JavaScript is not strictly an interpreted language, but rather a JIT compiled language. This means that the code is compiled at runtime, but only the parts of the code that are actually executed are compiled. Understanding the difference between compiled and interpreted languages is important for understanding how code is executed and optimized.