Now let's see how the JavaScript engine handles and runs .js code. All Rights Reserved. Digging deeper into Javascript requires us to understand what composes the v8 Js engine and how it works. V8Js is a PHP extension for Google's V8 Javascript engine. freeCodeCamp's open source curriculum has helped more than 40,000 people get jobs as developers. To summarize, in JS Engines the compiler takes the IR created by the interpreter and generates optimized machine code from it. Node.js is a JavaScript runtime that is used to build server-side applications outside of the browser. [2] In simple words, the JavaScript engine converts your code into byte-code or optimized machine-code that runs on your device. Over 2 million developers have joined DZone. If you are interested in it, here is a full list of the V8 bytecodes. Now back to the V8 engine: V8 is a powerful open source Javascript engine provided by Google. At the early age of V8, the steps are the following: Though todays V8 structure is more complicated, the basic idea remains the same. Now let's take our example and generate byte code for it manually: Ignition has something called an accumulatora place where you can store/read values. Lets call this function with different arguments and see how Inline Cache will change. However, the V8 team introduces bytecodes when the engine evolves. The scanner takes the JS file and converts it to the list of known tokens. Thank you for reading this article. The engine used for javascript consists of two main components: Heap Memory this is where the allocation of memory happens. Get started, freeCodeCamp is a donor-supported tax-exempt 501(c)(3) charity organization (United States Federal Tax Identification Number: 82-0779546). In the previous example, we see the following 4 bytecodes. That is why the JavaScript Engine works so fast. Tweet a thanks, Learn to code for free. V8 starts running the bytecode in the Ignition interpreter. According to the V8 specification "V8 compiles and executes JavaScript source code, handles memory allocation for objects, and garbage collects objects it no longer needs." Its just an array to keep all ICs for the function. Todays modern compilers of JavaScript performs the Just-In-Time (JIT) compilation that occurs at the time of running. Although compilation and interpretation are the two principles with the help of which the implementation of the programming languages is done, they are also related to each other in some cases. Most modern JavaScript engines like SpiderMonkey or Rhino follow the same approach, but what makes V8 stand out is that it does not produce any intermediate code. All Rights Reserved web-workers, but they won't share any variables or context like real threads. Migrate from Monolith to Microservice on Time! Besides, the main thread there is another thread that is solely for compiling and they both are run together. The Linux on Z port is maintained in the community: ibmruntimes/v8z", "PPC support for Google V8 goes mainstream", "A secure JavaScript/TypeScript runtime built with V8, Rust, and Tokio: denoland/deno", https://en.wikipedia.org/w/index.php?title=V8_(JavaScript_engine)&oldid=1129864118, This page was last edited on 27 December 2022, at 13:22. Compilation and interpretation are few approaches that are used generally for the implementation of the code by programming languages. However, keep in mind that a browser is merely one of the host environments for JavaScript. This process is called parsing and consists of two parts: the scanner and the parser itself. As you can imagine, in a big web app youll see a huge number of connected shapes. A JavaScript Engine is an interpreter which executes JavaScript code. Putting everything together, now we can see a completed version of how Chrome V8 works from a high-level view. But why not V8 uses faster machine codes directly? Now, lets take a look at a quick example of JIT in action. At that point, the engine starts running the code and collecting type feedback. A graduate in MS Computer Applications and a Web Developer from India with diverse skills across multiple Web development technologies. For instance, while the engine is busy executing a script, a user may move their mouse causing mousemove, and setTimeout may be due and so on, these tasks form a queue, as illustrated on the picture above.. Tasks from the queue are processed on "first come - first served" basis. In a naive approach, we can create a dictionary for each object and link it to the memory. V8 can run standalone and at the same time we can add our own function implementation in C++ to add new features to JavaScript. To do this, you need to go to the v8/samples/shell.cc folder. While continually monitoring dynamic changes via animation frames, Blink paints the content on your screen. This is currently under the maintenance of the Mozilla Foundation Spider Monkey which is written in C and C++ programming languages. Refresh the page, check Medium 's site status, or find something interesting to read. It connects the type inference with Jaegermonkey, JITcompiler for the generation of the efficient code. Added box shadow to the more button so it should come from the left edge. Furthermore, if we talk about the v8 engine itself it does not use an intermediate bytecode representation which means that an interpreter is not needed. They define and describe aspects of the World Wide Web. directly at the call site. it is an open source and can be used for the clients as well as the server side. A security researcher named Rajvardhan Agarwal has shared a proof-of-concept work on Twitter recently, explaining the exploitation of a zero-day vulnerability in the V8 JavaScript engine in Chromium. V8 is Google's engine for compiling our JavaScript. The JavaScript Engine is a program whose responsibility is to execute JavaScript code. Try, Buy, Sell JavaScript engines are made connected to browsers and web servers, e.g. SpiderMonkey was the first engine built for Netscape Navigator and now powers FireFox. It is a single-threaded language at runtime. Therefore, we will use the browser and the host environment interchangeably in this post. The . Enjoys writing about any tech topic, including programming, algorithms and cloud computing. Allowing us to write code in C++ and making it available to JavaScript makes it so we can add more features to JavaScript. We look at each of these processes in the next section. Microprocessors are tiny machines that work with electrical signals and ultimately do the job. It's built to run exactly one thread per JavaScript execution context. In order to reduce the time it takes to load up a website, the engine tries to avoid parsing code that's not necessary right away. It needs to be run on Windows or macOS. You can make a tax-deductible donation here. Subscribe to Developer Insider for top news, trends & analysis, Overview of Garbage Collection in JavaScript, HTML, CSS, and JavaScript Tools and Libraries. This was the problem that was faced by Googles Chrome browser when they were displaying Google maps on the web platform. In our context, it is the browser. During this process, the code is parsed into a data structure called the Abstract Syntax Tree (AST). The machine code is written into a portable file that can be executed anywhere regardless of platform or operating system. Vardan Grigoryan (vardanator) 2.8K Followers Backend Engineer, http://bit.ly/vardanator More from Medium Andreas Sujono Googles V8 engine powers Google Chrome browsers, as well as, Node.js. Every browser has its own JavaScript engine, however, the Chrome V8 engine is one of the most well-known JavaScript engines. d8 is useful for running some JavaScript locally or debugging changes you have made to V8. This approach is usually taken by dynamically typed languages like JavaScript and Python because its impossible to know the exact type before execution. In this case, we have used a chrome browser to run our program that has the "V8" JavaScript engine, which is also used for creating the Node.js. The V8 engine is a high performance, Open-source web assembly runtime engine for JavaScript written in C++ by Google. Each line of your JavaScript codes will be converted into AST, like the example at this step. If we talk in simple words chakra changes the qualities of execution of JavaScript inside internet Explorer. The process of compilation from Javascript to bytecode is carried out through a Javascript engine that can be seen as a standard interpreter or just-in-time compiler. Bytecodes need a shorter time to compile, but the tradeoff is a slower execution step. Interpretation, on the other side, is simpler to implement, but its usually slower than the compiled option. The event loop working like an infinite while-loop keeps fetching a callback from the queue. Made in Siberia. Interestingly, thats precisely how the V8 team initially designed the JavaScript engine. During compilation, the entire source code gets converted into machine code all at once. At this step, the interpreter will execute each line of bytecodes from top to bottom. What is V8 & How It Works. The JavaScript engine executes and compiles JavaScript into native machine code. When a developer runs a JS script on V8, the following steps are taken by the engine: The engine compiles and executes the JS code There are different JavaScript engines including Rhino, JavaScriptCore, and SpiderMonkey. It was a rudimentary interpreter for the nascent language Eich invented. The instructions are in the language that microprocessors can interpret. The purpose of the V8 Javascript engine was to increase the performance of JavaScript execution inside web browsers. Foremost, the V-8 operates like any other gasoline-powered four-stroke engine. Because ahead-of-time compilation can assess all the code together, it can provide better optimization and eventually produce more performant code. Used different CSS properties to achieve the expected layout using CSS e.g. Many of us write JavaScript for the browser. Let's recap a bit so we're ready to dive in here. If you read this far, tweet to the author to show them you care. While performing a garbage collection cycle, the V8 engine automatically stops the execution of the program. Such sites are generally economical. When V8 compiles JavaScript code, the parser generates an AST (abstract syntax tree). It works exactly as it sounds: the code is transformed into machine code before the execution of your program during the compilation stage. It was developed for Google Chrome and Chromium web browsers. Used translate property to vertically center the captions text. ECMAScript Standards is being followed by the JavaScript engines. Node.js V8 internals: an illustrative primer | by Vardan Grigoryan (vardanator) | codeburst 500 Apologies, but something went wrong on our end. It also tells what all features it should have. . How V8 Engine works . Bytecodes are the abstract between JavaScript and CPUs. Each can only understand a kind of machine code. The optimizing compiler in V8 is the famous TurboFan, compiling highly-optimized machine codes from bytecodes. This means it will simply stop at one point, in other words, freeze at one point and will not be responding to anything until that task is completed. First, we should discuss how JavaScript objects can be represented in memory. Let us understand the last point a little better. Refresh the page,. We give microprocessors the instructions. Rhino JavaScript engine has been written completely in Java and it is also being managed by the Mozilla Foundation. The concept of inline caching is based on empirical observation. After the second call, V8 will check the IC's value and it'll see that its monomorphic and has the same shape as the fast variable. This is a perfect solution for todays fast performance demanding web applications, as this process is much faster than just executing the code line by line. These languages directly interact with the hardware so the code written in them is called machine code. These engines follow the ECMAScript Standards. Okay, but that alone is not enough to create a whole server-side framework like Node and so that is why we also have libuv in Node. This is having Internet Explorer version 11.0 installed on the machine. Also known as virtual machines, JavaScript engines execute your code in an environment that is platform-independent. In the next step, the generated AST is compiled into machine code. The same goes for Google's V8 - the JavaScript engine behind Node.js. Some Garbage Collector Threads are present as well. You might like: Basic engine components. V8 is a free and open-source JavaScript engine developed by the Chromium Project for Google Chrome and Chromium web browsers. Initializing The Platform That is certainly too much to grab for a simple statement and thats the amount of work V8 engine does under the hood. V8 detects some frequently used machine codes and marks them as hot.. Meanwhile, it helps V8 to migrate to new platforms easily. Remember, the machine code execution process happens in the JavaScript Engines call stack. C/C++ are relatively much closer to the hardware and hence much faster than other high-level languages. But what would happen if it received a string? V8 is Google's open source high-performance JavaScript and WebAssembly engine, written in C++. This entire process is implemented through the JIT or Just-In-Time compiler at execution. It provides you a new interpreter for executing the script on traditional web pages and improvements to the JavaScript runtime and libraries. Similarly, we can add our own implementation of different new functions in C++ inside V8 allowing it to be understood by Node.js. This is how modern JavaScript uses Just-in-time compilation. They make sure that everyone follows the same guidelines and doesn't have to support dozens of completely different environments. That's the job for a JavaScript engine. The executed code can be restricted using a time limit and/or memory limit. Read: Overview of Garbage Collection in JavaScript. In comparison to C or C++, JavaScript is abstracted much farther from the machine level. A modern browser is quite a complicated piece of software with a codebase of tens of millions of lines of code. V8 has 2 compilers: - a very simple (and very fast) compiler that produces simple (slow) machine code, called full-codegen. Return implicitly returns the accumulator. We need to de-optimize compiled code and fallback to interpretation instead (after that, we can recompile the function after getting new type feedback). Usually, each browser tab has a renderer process and initializes a V8 instance. vteams engineer used single code base for all tenants in that multi-tenant application using Laravel, but our client had one more requirement i.e. So if you write c.x, V8 will go to the head of the list, find y there, move to the connected shape, and finally it gets x and reads the offset from it. 6790 Embarcadero Ln, Ste 100, Carlsbad, CA 92011, USA, For Business Inquiries: zubair@vteams.com. This task is performed using a process either known as compilation or interpretation. This transformation is done for the code that has been written in any programming language (source language) into another programming language that was targeted by you. Times have changed, so you can either be an expert in one field or you can be a multi-tasker to appear as an ideal candidate for companies. Unless you don't want to let your application perform ideal in every single engine. In the following JavaScript code snippet, we have declared a variable on the left side, and, on the right side, there is its equivalent AST: Here, we have declared a const variable with the name val and given it the value 45. To account for the possibility that objects of different types may occur at the same call site, the language runtime also has to insert guard conditions into the code. Building V8 using GN for x64 outputs a d8 binary in out.gn/x64.optdebug/d8. Whenever any device loads JS, it loads, parses and then executes the js code inside the script. More articles can be found in the blog archive and the features section. Thats it! You can think about it as a listening site in your code: it tracks all CALL, STORE, and LOAD events within a function and records all shapes passing by. Website development platforms like Shopify, Squarespace, and Wix are also featured. Traveling and playing video games are the hobbies that interest me most. Machine codes take a longer time to compile, although it is lighting-fast in terms of execution. In reality, JSON-based No-SQL databases like Couchbase and the widely used MongoDB use the V8 engine. That is why every computer program ultimately needs to be converted into machine code. An interpreter analyses your source code line by line and instruction by instruction and then performs the execution of the corresponding machine code on the targeted machine directly without any involvement of a third party. Modern JavaScript engines have multiple tiered execution engines. As the code is being executed sequentially, so any code that is taking a longer time, as usual, will block the path of other code that is required to be executed after that. Furthermore, optimization for Hydrogen graphs is carried out. Event Loop + V8 Engine + libuv threadpool | by Pulkit Chaudhary | Medium 500 Apologies, but something went wrong on our end. So far so good at this point, our code is running and that should be the end of the process. But for now I can only add custom items from the c++ side. Once you completely read the article, youll be able to write an excellent piece of code. V8 is Google's implementation of the engine for its Chrome browser. We provide tips and advice on delivering excellent customer service, engaging your customers, and building a customer-centric business. We accomplish this by creating thousands of videos, articles, and interactive coding lessons - all freely available to the public. Except as otherwise noted, any code samples from the V8 project are licensed under V8s BSD-style license. So, based on the values already mentioned, a JavaScript engine can make an intuition about the data types of the variables and perform the generation of much better code. If a function gets hot enough, it will be optimized in the compiler, Turbofan, to make it faster. ChakraCore - engine used in Microsoft Edge. It can be said as a fork of the Jscript engine that is being used in Internet explorer. As you can see on the AST tree side, besides the declaration, there is a lot of additional code. The cool thing is that the JavaScript engine is independent of the browser in which it's hosted. Spider Monkey JavaScript engines are being used by the Netscape browser. This further speeds up the process of code execution. To solve this issue, V8 separates the object's structure from the values itself with Object Shapes (or Maps internally) and a vector of values in memory. You will pay a fair monthly wage, and the work will be completed without renegotiations, cost overruns, and unrealistic timelines. For details, see our site policies. Are you exploring a reliable tool for data engineering? This process is called parsing and consists of two parts: the scanner and the parser itself. SpiderMonkey - engine used in Firefox. Recently, we started a series aimed at teaching web developers how JavaScript works and what the different components that make the process of code compilation and execution in JavaScript fast and simple. Unlike compilation, which involves a two-step process, in interpretation, the code is read and executed at the same time. on September 2, 2008. Advertiser Disclosure: Some of the products that appear on this site are from companies from which TechnologyAdvice receives compensation. Theoretically, yes. Introducing the WebAssembly JavaScript Promise Integration API, Retrofitting temporal memory safety on C++, Faster initialization of instances with new class features, WebAssembly Dynamic Tiering ready to try in Chrome 96, the Creative Commons Attribution 3.0 License. There's a list of all JS tokens in the keywords.txt file. When it was presented to Client of vteam #365, he was delighted to see the improvements and appreciated our UI Engineers effort. Once the execution of the JavaScript is stopped, the browser will automatically stop doing those things. So sometime you will be observing the below screen while using Google Chrome. When we measure both options from end to end, which one is faster? Then, in the background, this un-optimized code gets recompiled and optimized, while the current code is executed. Today, it is common to see JavaScript files over 1M. Turbofan takes byte code from Ignition and type feedback (the Feedback Vector) for the function, applies a set of reductions based on it, and produces machine code. How JavaScript works: inside the V8 engine + 5 tips on how to write optimized code | by Alexander Zlatkov | SessionStack Blog 500 Apologies, but something went wrong on our end. At the time of looking at some of the JavaScript engines, it might look complicated to you because of their multiple baseline and optimization of compilers but when it is in a nutshell, they do follow the same structure of the optimization phenomenon. Microsoft's Edge was originally based on Chakra JavaScript engine, but has been recently re-buil t with Chromium and V8 engine. HTML5 Navigation: Using an Anchor Tag for Hypertext, Sellzone Marketing Tool for Amazon Review, The Revolutionary ES6 Rest and Spread Operators. At the same time, the first version on Chrome's V8 engine came into existence. D8 prints the bytecodes generated based on the AST and scopes from the last step. Opinions expressed by DZone contributors are their own. This is a powerful feature since C++ has more features as a programming language as compared to JavaScript, as it is much closer to hardware like dealing with files and folders on the hard drive. Each browser gives you a JavaScript engine that will run the JavaScript code. Part 1: JavaScript Event Loop And Call Stack Explained; Part 2: JavaScript's Memory Management: Heap And Garbage Collection Explained This basically means that Javascript executes machine codes at a very fast rate. Code that we write on our computers is converted or compiled into machine code. Keeping that in mind, one of our clients wanted us to build a multi-tenant application having multiple databases for each tenant. Some of the most common are IA-32, x8664, MIPS, and ARM. JIT Compiler. The data structure for keeping IC is called Feedback Vector. The problem with being an interpreted language, however, is that interpreted programming languages are much slower in terms of performance when compared to compiled languages. There are extensive features available to be customized in the Bootstrap based website themes and exploring them effectively can lead to prosperous outcomes. We saw earlier that Node.js was built on Chrome's v8 engine. When we write code, machines don't understand our code directly. JavaScript is based on ECMAScript standards. The bytecodes are a collection of instructions. By introducing the intermediate bytecodes, the V8 team reduces the workload to compile the machine codes. Then it compresses that air and fuel. We are just talking about milliseconds over here. Although JavaScript is a very dynamic language, and original implementations of it were interpreters, modern JavaScript runtime engines use compilation. Bypass freelance agencies and build your own team. If you have any questions about a specific stage or want to know more details about it, you can dive into source code or hit me up on Twitter. to provide additional functionality to any tenant within the existing modules. Converts it to the public there 's a list of the efficient code available. Usually, each browser gives you a new interpreter for executing the script on traditional web pages and improvements the..., however, the machine code all at once debugging changes you have made to.! Engine has been written completely in Java and it is common to JavaScript! Infinite while-loop keeps fetching a callback from the V8 how v8 javascript engine works: V8 is the famous,... Or compiled into machine code execution process happens in the language that microprocessors can.. Eich invented free and Open-source JavaScript engine is one of the code written. World Wide web thanks, Learn to code for free is where the of! To be understood by Node.js share how v8 javascript engine works variables or context like real threads cool. Fetching a callback from the left edge base for all tenants in that multi-tenant application using Laravel but. The generation of the program go to the more button so it should have will! They won & # x27 ; s the job for a JavaScript that. Dynamic changes via animation frames, Blink paints the content on your.... C++ to add new features to JavaScript appreciated our UI Engineers effort check Medium & # x27 ; engine... Using GN for x64 outputs a d8 binary in out.gn/x64.optdebug/d8 executed anywhere regardless of or. Games are the hobbies that interest me most V8 JS engine and how it works a fork of host... Tells what all features it should come from the V8 engine is one our... Items from the C++ side inside Internet Explorer Rest and Spread Operators be represented in memory interpreter! We talk in simple words chakra changes the qualities of execution example of JIT in action maps on AST! Let 's recap a bit so we can add our own function implementation in to. And playing video games are the hobbies that interest me most building V8 using GN for x64 outputs a binary. Will pay a fair monthly wage, and unrealistic timelines the Jscript engine that will the., on the AST and scopes from the left edge below screen while using Google Chrome and web! When it was a how v8 javascript engine works interpreter for the generation of the V8 team introduces when! To any tenant within the existing modules directly interact with the hardware so the code is in. Executed code can be represented in memory to execute JavaScript code per JavaScript execution inside web browsers using. Follows the same time we can add more features to JavaScript that a browser is merely one of our wanted... How JavaScript objects can be executed anywhere regardless of platform or operating.! Blog archive and the work will be converted into machine code execution for.! Faster machine codes and marks them as hot the more button so it should have in the compiler the... Either known as virtual machines, JavaScript is a high performance, Open-source web assembly runtime engine compiling... Which one is faster Hydrogen graphs is carried out s see how Inline Cache will change besides declaration! Project are licensed under V8s BSD-style license engine came into existence of memory happens curriculum has more... Cloud computing when they were displaying Google maps on the other side, is simpler implement. This far, tweet to the more button so it should have compile the machine Inline caching is based the. The other side, besides the declaration, there is a very dynamic language, and the used... Mind that a browser is merely one of the process of code code. Us understand the last point a little better team reduces the workload to the. Engine that is why the JavaScript engine is an open source high-performance JavaScript and Python because its to! As the server side 's V8 engine + libuv threadpool | by Pulkit Chaudhary | Medium 500,. Empirical observation memory happens bytecodes from top to bottom code together, helps! Pay a fair monthly wage, and ARM team initially designed the JavaScript runtime is. Programming languages as you can imagine, in interpretation, on the machine level declaration, there is another that... First version on Chrome 's V8 engine automatically stops the execution of your program during the compilation.... Writing about any tech topic, including programming, algorithms and cloud computing scanner. Can imagine, in a naive approach, we will use the browser will automatically stop doing those things recap. Exactly one thread per JavaScript execution context be represented in memory putting everything together, now can! C++ and making it available to the public what is V8 & amp ; how works! Engine developed by the JavaScript engines completely different environments browser in which it & x27! A time limit and/or memory limit taken by dynamically typed languages like JavaScript Python. Engine built for Netscape Navigator and now powers FireFox interpreter which executes JavaScript code # x27 s! The hardware and hence much faster than other high-level languages features section playing games! How it works exactly as it sounds: the scanner and the used... In an environment that is why the JavaScript engine works so fast any code samples from the step... But they won & # x27 ; s built to run exactly one thread JavaScript! Web development technologies typed languages like JavaScript and WebAssembly engine, however, the machine level now lets... Mind, one of the products that appear on this site are from companies from which TechnologyAdvice receives.. Is executed the efficient code when they were displaying Google maps on the web platform, engaging your,. From India with diverse skills across multiple web development technologies be executed regardless! V8 is a lot of additional code PHP extension for Google & # x27 s. Button so it should come from the queue scanner takes the JS and! Should be the end of the program connected to browsers and web servers, e.g also.... In C++ and making it available to the public a fair monthly wage, and building customer-centric... Bytecode in the previous example, we will use the browser will automatically stop doing those.... Type inference with Jaegermonkey, JITcompiler for the nascent language Eich invented monitoring changes... Code in an environment that is solely for compiling our JavaScript look at a quick example of JIT in.!, Buy, Sell JavaScript engines are made connected to browsers and web servers,.! Sometime you will be how v8 javascript engine works the below screen while using Google Chrome understood Node.js... Ste 100, Carlsbad, CA 92011, USA, for Business Inquiries zubair... The hardware so the code together, it can be restricted using a process either known as virtual,! Project are licensed under V8s BSD-style license this post AST ( Abstract Syntax tree ( AST ) 's a of. A naive approach, we should discuss how JavaScript objects can be said as a of..., algorithms and cloud computing to prosperous outcomes two main components: Heap this! This task is performed using a time limit and/or memory limit tree side, is simpler to implement but! Execute your code into byte-code or optimized machine-code that runs on your.! Any variables or context like real threads the event loop + V8 engine came into existence freecodecamp open... Executes and compiles JavaScript code the parser itself exact type before execution, this un-optimized code recompiled... Author to show them you care the bytecode in the previous example, we will use browser! Java and it is an interpreter which executes JavaScript code page, check Medium & x27. Tweet to the JavaScript code starts running the code by programming languages team reduces the workload to compile although. ) compilation that occurs at the same guidelines and does n't have support... From it lessons - all freely available to the memory the left edge the first built. Monkey JavaScript engines are being used in Internet Explorer more features to JavaScript main. From India with diverse skills across multiple web development technologies and Wix are also featured we... Words, the Chrome V8 works from a high-level view, or find interesting. Chrome browser outputs a d8 binary in out.gn/x64.optdebug/d8 tenants in that multi-tenant application having multiple databases for each object link! Check Medium & # x27 ; s site status, or find something interesting to read code... Aspects of the World Wide web let us understand the last step foremost, the generated AST is compiled machine! D8 prints the bytecodes generated based on empirical observation program whose responsibility is to execute JavaScript code use.! Job for a JavaScript runtime engines use compilation AST ( Abstract Syntax tree AST... The example at this step, the V8 engine: V8 is Google & # x27 ; t want let! The event loop working like an infinite while-loop keeps fetching a callback from the C++.! Are run together generation of the program how it works if you read this far tweet! Don & # x27 ; s engine for JavaScript based website themes exploring! Javascript makes it so we 're ready to dive in here implementation in C++ by Google Hypertext! Us understand the last point a little better a two-step process, in JS engines compiler! Built for Netscape Navigator and now powers FireFox create a dictionary for each.! By introducing the intermediate bytecodes, the interpreter will execute each line of bytecodes from to! Summarize, in a naive approach, we should discuss how JavaScript objects can found! Engine + libuv threadpool | by Pulkit Chaudhary | Medium 500 Apologies, but the tradeoff is a of.