The Basics of Javascript

javascript is the scripting language used to add interactivity and animations to web pages. Web browsers include a special engine that reads, interprets and executes javascript. The engine is called a JavaScript virtual machine. The most common VM is V8, but other engines like Chakra for Internet Explorer and SquirrelFish for Safari and Edge are available.

The first step a web browser takes when it encounters javascript is to parse the code. This is a process that breaks the javascript into its constituent parts such as keywords, variables and functions. The resulting data structure is known as an Abstract Syntax Tree or AST. This AST is what the javascript engine uses to generate machine code that will be executed.

When the AST is parsed, it is stored in memory and a call stack is created. The call stack is a list of all functions that have been invoked, and the function that is currently being executed will be at the top of this list. This is because javascript runs in a single-threaded manner. This means that only one instruction is executed at a time, even if the CPU has multiple cores and available threads.

Aside from these fundamental concepts there are a few key features that make javascript unique. It is a multi-paradigm language that supports object-oriented programming with class and prototype objects, as well as functional programming through functions being first-class objects. It also supports a type system, with standard built-in types such as int, float and bigint. The javascript language also has a rich set of error handling capabilities, with multiple built-in types such as Error and RangeError for defining the different possible errors that can be encountered.

In addition to the aforementioned features, javascript also supports several other advanced technologies and techniques. Event delegation is a technique for managing multiple events from a single event handler. Prototypal inheritance allows a new object to inherit properties and methods from another object. The javascript language is also very dynamic, meaning that it does not enforce a strict typing system and the true types of variables are only determined at runtime.

The aforementioned features make javascript a powerful and versatile web development language that is commonly used in front end and back end web applications. For example, front end web developers use javascript to develop interactive features such as image sliders and games while back end web developers use it to optimize web pages for performance. Since javascript is client-side it can be used to reduce server load by performing data validation in the web browser and providing updates that only affect certain sections of the web page. This can save valuable computing resources and improve user experience. In addition, because javascript is client-side it can take advantage of the Document Object Model (DOM) to access and manipulate web page elements such as text, images and form fields. For this reason, javascript has become a ubiquitous part of modern web development.