The browser is capable of executing code because it contains a JavaScript runtime environment. Unlike a machine, a JavaScript engine can be thought of as a set of code written in a low-level language.

JavaScript Interpreted or Compiled?

• JavaScript is a versatile language that can be interpreted or compiled based on the JavaScript engine used. It's Just-in-Time (JIT) compilation capability allows the engine to dynamically choose between interpretation and compilation, making JavaScript a Just-in-Time compiled language.

Code Execution in the V8 JS Engine

Step 1️⃣ : The code undergoes parsing, where it is divided into tokens, and subsequently, the syntax parsing phase transforms the code into an Abstract Syntax Tree (AST).

• After the Abstract Syntax Tree (AST) is formed, it proceeds to the compilation phase, where JavaScript employs Just-in-Time (JIT) compilation techniques.

Step 2️⃣ : The AST (Abstract Syntax Tree) generated from the code is passed to the interpreter, which converts the high-level code into bytecode, allowing it to progress to the execution phase.

• During this process, the interpreter works in collaboration with the compiler to optimize the code, performing line-by-line optimizations at runtime. This optimization is a multi-phase process, as JavaScript engines utilize their own algorithms for achieving optimal performance.

Step 3️⃣ : JavaScript engines employ an approach called Ahead-of-Time (AOT) compilation, where the compiler optimizes a future code segment to its maximum potential. This optimized code is converted into bytecode and subsequently executed.

Step 4️⃣ : JavaScript execution depends on the memory heap and the call stack. The memory heap acts as a storage area where memory is allocated for variables and functions.

• The garbage collector plays a vital role by releasing memory space when it becomes unused, employing techniques like the mark and sweep algorithm to identify and clean up functions that are no longer in use.

• Compilers perform various forms of code optimization, including inlining, copy elision, and inline caching. These optimizations enhance code performance and efficiency.

The Google Chrome V8 JavaScript engine comprises two components: Ignition, which acts as an interpreter, and Turbofan, which serves as a compiler. Together, these components significantly enhance the speed and efficiency of code execution, resulting in faster performance.