JavaScript and Just In Time Compiler

Programs that we write using any programming language like C, JavaScript, etc. are "High-level" programming languages. A high-level programming language is a language that is designed to be easily understood by humans and to be independent of a particular type of computer or architecture. In other words, high-level languages are designed to be closer to human language than to the machine code that computers understand. The conversion of a high-level language to machine code can be done by using compilation or interpretation.

What is Machine Code?

Machine code is the lowest-level programming language that computers can directly execute. It consists of binary code, which is a series of 0s and 1s, representing specific instructions that the computer's central processing unit (CPU) can directly understand and execute. Each instruction in machine code corresponds to a specific operation, such as arithmetic calculations, data movement, or control flow

What is JIT Compilation?

So, imagine you're throwing a party and you want to make sure there's enough food for everyone. You could either cook all the food in advance, guessing how much each person will eat, or you could prepare dishes as people arrive, ensuring everything is fresh and no food goes to waste. The first approach is like traditional compilation, where code is translated all at once before execution. The second approach is similar to just-in-time (JIT) compilation.

In JavaScript, a just-in-time compiler works by translating code into machine code or an intermediate representation at runtime, just before it's executed. This contrasts with ahead-of-time (AOT) compilation, where code is translated before it's run. JIT compilation allows for optimizations tailored to the specific execution environment and can adapt to runtime conditions.

When you load a web page, the JavaScript code is usually initially interpreted by the browser's JavaScript engine. However, for performance reasons, modern engines like V8 (used in Chrome) often employ a combination of interpretation and JIT compilation. The engine analyzes the code as it runs, identifying hot paths—frequently executed code—and compiles them for more efficient execution.

This approach has its advantages. The compiled code is optimized based on actual usage patterns, making it more tailored to the environment it's running in. Additionally, it allows for quicker startup times compared to fully precompiled languages.

So, just-in-time compilation is like having a chef in the kitchen during your party, preparing dishes on demand to ensure everything is served fresh and nothing goes to waste!