WEB JAVASCRIPT ENGINE

A JavaScript engine is the software that parses compiles and executes JavaScript code. It translates human readable JavaScript (JS) code into machine instruction the CPU can run. Thus the JavaScript engine is the brain. It handles parsing and compiling JavaScript code, running logic calculations and functions, manipulating the DOM (adding and removing elements), handling events (clicks, key presses) and fetching data from servers .

There are several types of JavaScript web engines and they are; spider monkey, V8, JavaScript core, Hermes, chakra and Jscript JavaScript web engines.

Spider monkey JavaScript web engine is maintained by Mozilla and serves as the JavaScript engine for Firefox, with gecko as its rendering companion. It performs particularly well in workloads involving heavy DOM manipulation, making it an excellent partner for Geeko’s parallel rendering pipeline. Beyond Firefox, spider monkey is notable for being embedded in non-browser applications. For instance, mongo DB uses it as its query scripting engine. Its primary limitations are that its raw computational throughput trails slightly behind V8 in most benchmark test. When spider monkey executes JavaScript that modifies the page, Geeko’s web render GPU pipeline repaints the results with impressive efficiency.

V8 is Google’s JavaScript web engine. V8 introduced just-in-time compilation into mainstream browser JavaScript execution, delivering performance improvement that made previously impossible web applications suddenly feasible. V8 JavaScript web engine powers not only chrome and edge, but also node.js, deno and electron, making it the engine behind much of both client-side and server-side JavaScript execution globally. However V8’s greatest weakness is its high memory consumption, a consequence of its aggressive optimization strategies and multi-process architecture. Also its complex JIT pipeline may lead to unpredictable performance behavior. Nevertheless V8 remains the benchmark against which all other JavaScript engines are measured.

JavaScript core is the JavaScript engine powering safari on all apple platforms and all ios web views. It is also the engine behind Dun, one of the fastest JavaScript runtimes available today outside the browser. JavaScript core optimizes for memory efficiency and battery life, the two most critical concerns for mobile device users.

Hermes is Meta’s JavaScript web engine. It represents a different approach from other JavaScript web engines. Rather than using just-in-time compilation to optimize code at run time, Hermes precompiles JavaScript into byte code at build time, before the application is installed on a user’s device. This approach trades peak execution performance for dramatically faster application start up times and significant lower memory consumption, both of which are critical priorities for mobile applications. Hermes does not partner with a traditional web rendering engine instead it works alongside react natives own rendering system, which renders application interfaces using native platforms components rather than web technologies. This makes Hermes unique amongst major JavaScript engines.

Chakra was Microsoft’s JavaScript engine, developed to accompany EdgeHTML as its rendering engine partner. It represented a significant improvement over Jscript, the aging engine used in internet explorer with trident. Chakra featured a multi-tier just in time (JIT) compilation pipeline, a concurrent garbage collection and reasonable standard compliance, delivering competitive performance during its brief operational life.

Jscript was Microsoft’s proprietary JavaScript web engine used in internet explorer alongside the trident rendering web engine. It was Microsoft’s implementation of JavaScript, compatible enough to run basic scripts but diverging from standards in important ways that caused cross browser compatibility problems for developers leading to the demise of Jscript as JavaScript web engine of choice.

The advantages of JavaScript web engine are; JavaScript web engines provide for universal execution environment, where code runs across browsers, servers, mobile apps, IoT devices and desktop software, making JavaScript one of the few languages that’s genuinely ‘write once, run almost everywhere’. Web engines are built to handle JavaScript’s dynamic typing, prototypal inheritance and run time flexibility without sacrificing too much performance, thus enabling developers iterate quickly without a compile step of their own. JavaScript engines enables just in time compilation, such that modern web engines compiles hot code paths to optimized machine code on the fly, so performance critical applications can run at nearly the compiled language speeds, despite JavaScript being interpreted at heart. JavaScript engines provides for automatic memory management, thereby reducing entire classes of bugs (memory leaks, dangling pointers) common in lower level languages. Also JavaScript engines have massive ecosystem leverage, because engines like V8 powers both browsers and node.js, the same language and many of the same libraries work on front end and back end, thus collapsing the traditional client/server skill divide. JavaScript engines execute untrusted code from the web in isolated environment, thereby preventing malicious scripts from execution.

The disadvantages of web JavaScript engines are; web JavaScript engines performances depends on the work load and can be unpredictable. Web JavaScript engines consume vast amount of memory, which adds up fast across many browser tabs or large server processes. Web JavaScript engines de-optimize engines runtime penalties, a performance limitation that is hard for developers to predict. Web JavaScript engines exhibit inconsistent behavior across engines making ‘write once, run everywhere’ imperfect in practice. Web engines execute arbitrary code from untrusted source by design making JavaScript engines prone to security surface attacks. Web engines complexity adds maintenance burdens as a result of its full compiler tool chain (multiple JIT tiers, garbage collectors, byte code formats), make them not only expensive to build, maintain and audit.

The applications of JavaScript web engines are as follows; JavaScript web engines are used in web development to create dynamic web pages, single page applications and progressive web apps. JavaScript engines are used in desktops and mobile applications such as electron and react native, to build cross platform applications. JavaScript engines, such as node.js are used for server side programming, enabling developers to build a scalable and high performance server side applications. JavaScript engines are used in machine learning and artificial intelligence applications, such as tensor flow.js, brain.js and so on.

The future of JavaScript web engines is based on the advances and development of the following technologies; JavaScript engines will continue to improve performance, prioritize security and support web assembly, a binary instruction format that enables near native performance for web applications and progressive web apps (PWA), which will provide a native app-like experience for web users. JavaScript web engines, will be adopted and integrated with AI and ML applications, enabling developers to build more intelligent and interactive web applications.

 

SOURCES:

• Javascript engine architecture by Vitaly Friedman and Paul Irish.
• V8: Javascript engine for the masses by Lars Hansen and Christian Voldsted.
• Crafting interpreters by Robert Nystrom.
• Speaking javascript by Axel Rauschmayer.
• Web assembly: A guide to building high performance web applications by Nick Fitzerald.