The JavaScript engine has the ability to read, understand, and execute your code. It works like a converter that takes your code, turns it into instructions that the computer can understand and work accordingly.
One of the most well-known JavaScript engines is V8, developed by Google, used in Chrome and Node.js. The JavaScript engine works in a few steps. First, it parses your code, reading it line by line to make sure there’s no mistake in the JavaScript code. Then, it converts this code into bytecode, which is a simpler, intermediate version of your code that’s easier for the computer to understand and execute. Finally, it runs this bytecode to execute your program’s instructions. Here’s an example of JavaScript code:
const greeting = "Hello, World!";
console.log(greeting);When you run this code, the JavaScript engine first parses it to check for any syntax errors. Parsing means the engine reads the code and breaks it down into a structure it can understand, checking for mistakes along the way.
Then, it compiles the code into an intermediate format (often bytecode or machine code, depending on the engine). Compiling is the process of converting the human-readable code into a more efficient format that the computer can execute faster.
Finally, the engine executes the code, printing Hello, World! to the console.
Now, let’s talk about the JavaScript runtime. The JavaScript runtime is the environment in which your JavaScript code is executed. It includes the JavaScript engine (like V8 in Chrome or SpiderMonkey in Firefox), which processes and executes the code, as well as additional features provided by the environment (such as a web browser or Node.js, which you will learn more about in future lectures).
While the core JavaScript language handles things like variables, loops, and functions, the runtime provides extra tools that allow JavaScript to interact with things outside of the language itself, like the DOM (for web pages) or the Fetch API (for making network requests).
In short, the runtime is what allows JavaScript to do more than just basic programming tasks – like interacting with web pages or handling time-based actions – by providing these extra features beyond the language itself.
While you don’t need to know every detail of engines and runtimes to write JavaScript, having a basic understanding can help you write more efficient code and debug problems more effectively.