JavaScript is a programming language that runs on the web browser. It allows developers to turn static HTML web pages into interactive websites. It also lets them do things like validate form data, control multimedia, and animate images on the page.
The Basics
In the early days of the web, most web pages were static. That is, they didn’t have any graphical elements, animations, or other interactivity to them. However, a new programming language called JavaScript (now known as ECMAScript) was developed in 1995 by Brendan Eich to help turn these pages into more interactive ones.
A few years later, JavaScript grew to become the most important technology for creating web interfaces. It was a key part of the Ajax revolution that enabled web applications to load data in the background without having to reload the entire page.
Now, JavaScript is a very popular tool for web developers and is used on the front end of most website. It’s also a powerful tool for back end web development, such as building web servers or games.
Scripts run automatically within the web browser and don’t require any additional software to be installed or compiled before they can be used. This makes it easy for people to use JavaScript, even if they have no prior experience in coding.
When someone enters a piece of JavaScript code into the browser, it will be converted to an intermediate representation (IR), which is known as bytecode. It will then be passed to an interpreter and then executed.
It’s important to understand how a JavaScript program works when it’s being interpreted because that will make it easier to understand how it interacts with the web. Firstly, when a JavaScript code is being interpreted by the interpreter, it creates an Abstract Syntax Tree, which is a sort of tree diagram that illustrates how the program works.
Then, when the code is being interpreted, it creates an execution context for each line of the code that it is executing. This execution context contains all the variables that will be accessed when the code is being executed.
After this, it will execute the code one line at a time, using the execution context it created. It will then destroy the execution context when it is done completing all the lines of code that were executed.
This is a very complicated process and it’s why JavaScript has a built-in mechanism called Call Stack to keep track of this complexity. This stack manages how a function is created and destroyed when it’s being called by another JavaScript function, which can be nested inside it.
There are many other components that make up the JavaScript engine, which is present in most modern web browsers. These include a baseline compiler, which compiles the source code into bytecode and passes it to the interpreter.
A JavaScript interpreter will then take the bytecode and convert it into machine code, which will be run on the CPU. Conclusion: It’s a complex process, but it’s essential to understand how it all works.