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What is a V8 JavaScript engine?
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V8 is the JavaScript engine i.e. it parses and executes JavaScript code. The DOM, and the other Web Platform APIs (they all makeup runtime environment) are provided by the browser. The cool thing is that the JavaScript engine is independent of the browser in which it's hosted.
- V8 Engine Relies on and Empowers The Host Environment
- Compile Javascript Codes
- Generate Bytecodes
- Interpret and Execute Bytecodes
- Compile and Execute Machine Codes
- Bytecodes vs. Machine Codes
- Machine Codes Requires A Great Amount of Memory
- Machine Codes Are Not Always Faster Than Bytecodes
- Machine Codes Increases Complexity in Development
- Takeaways
The host environment to V8 is like your computer’s operating system to software. Softwares rely on the operating system to run. Meanwhile, they empower your system to do so many advanced tasks. Take Photoshop, for example. It needs to be run on Windows or macOS. Meanwhile, your operating system cannot make a beautiful poster for you, but Photoshop ...
At this step, the V8 engine converts the JavaScript codes to Abstract Syntax Tree (AST) and generates scopes. The V8 engine doesn’t speak JavaScript language. The script needs to be structured before processing. AST is a tree structure, easy for V8 to digest. Meanwhile, scopes are generated at this step, including the global scope and more scopes a...
At this step, the V8 engine takes the AST and scopes and outputs bytecodes. How do the bytecodes look like? Let’s use the same example, this time, with D8, the developer shell of Chrome V8. To install the D8 in macOS, run the following command in the terminal. Save our example codes in a javascript file v8.js, and run the following command in the t...
The bytecodes are a collection of instructions. At this step, the interpreter will execute each line of bytecodes from top to bottom. In the previous example, we see the following 4 bytecodes. Each line of the bytecodes is like a prefabricated block of Lego. No matter how fancy your codes are, all are built with these basic blocks behind the scene....
This step is parallel to the previous one. When executing the bytecodes, V8 keeps monitoring the codes and looking for opportunities to optimize them. When some frequently used bytecodes are detected, V8 marks them as “hot.” Hot codes are then converted to efficient machine codes and consumed by the CPU. What if the optimization fails? The compiler...
But why not V8 uses faster machine codes directly? Wouldn’t introduce intermediate bytecodes slow down the entire process? Theoretically, yes. But that’s not the whole story. Interestingly, that’s precisely how the V8 team initially designed the JavaScript engine. At the early age of V8, the steps are the following: 1. V8 compiles scripts to AST an...
The V8 engine stored complied machine codes in the memory to reuse them when the page loads. When compiled to machine codes, a 10K JavaScript could inflate into 20M machine codes. That’s about 2,000 times larger memory space. How about the size of the bytecodes in the same case? It is about 80K. Bytecodes are still more massive than the original Ja...
Machine codes take a longer time to compile, although it is lighting-fast in terms of execution. Bytecodes need a shorter time to compile, but the tradeoff is a slower execution step. An interpreter needs to interpret bytecodes before executing them. When we measure both options from end to end, which one is faster? It depends. The art is finding a...
Different CPUs could have various structures. Each can only understand a kind of machine code. There are a lot of processor structure designs on the market. To name a few: 1. ARM 2. ARM64 3. X64 4. S397 5. And more… If the browser only uses machine codes, it needs to take care of so many cases separately. As a developer, we know that’s not a good p...
Putting everything together, now we can see a completed version of how Chrome V8 works from a high-level view.
Aug 26, 2020 · August 26, 2020 / #JavaScript. How JavaScript Works: Under the Hood of the V8 Engine. Ilya Lyamkin. Today we’ll look under the hood of JavaScript's V8 engine and figure out how exactly JavaScript is executed. In a previous article we learned how the browser is structured and got a high-level overview of Chromium.
Jan 31, 2024 · What is V8? V8 is Google’s open source high-performance JavaScript and WebAssembly engine, written in C++. It is used in Chrome and in Node.js, among others. It implements ECMAScript and WebAssembly, and runs on Windows, macOS, and Linux systems that use x64, IA-32, or ARM processors. V8 can be embedded into any C++ application.
V8 is a JavaScript and WebAssembly engine developed by Google for its Chrome browser. V8 is free and open-source software that is part of the Chromium project and also used separately in non-browser contexts, notably the Node.js runtime system.
Feb 26, 2024 · The V8 JavaScript engine, developed by Google, is a high-performance open-source engine designed to execute JavaScript code efficiently. Initially created for the Google Chrome web browser, V8 has become a key component in various applications and platforms, showcasing its versatility.
Nov 3, 2023 · Since JavaScript is a single-threaded language (code is executed line by line), the V8 engine uses a single process per JavaScript context, and, for example, if you need service workers, it...
