How JavaScript Works
Learn in a simple way how JavaScript code moves from your program to the browser and finally produces a result.
The Basic Idea
When you write JavaScript code and open the web page, the browser receives your code and runs it using a JavaScript engine.
The JavaScript engine reads the code, processes it, and executes the instructions.
JavaScript code moves from the browser to the JavaScript engine and then gets executed.
Step-by-Step Process
Write JavaScript
The developer writes JavaScript code inside an HTML page or an external JavaScript file.
Browser Loads the Code
The browser loads the web page and prepares the JavaScript code for execution.
JavaScript Engine Processes It
The JavaScript engine parses and processes the code so that it can be executed.
Code Executes
The engine executes the instructions and produces the required result.
What is a JavaScript Engine?
A JavaScript engine is the software responsible for processing and executing JavaScript code.
Different browsers use different JavaScript engines. For example, Chrome and Chromium-based browsers use V8, while Firefox uses SpiderMonkey.
Simplified JavaScript engine processing pipeline.
Simple Example
Look at this small example. The browser executes the JavaScript code and displays the value in the console.
const number1 = 10;
const number2 = 20;
const total = number1 + number2;
console.log(total);Output
JavaScript and the Browser
The browser provides many features that JavaScript can use. For example, JavaScript can work with the page content, user events, timers, storage, and network requests.
Simple Example
JavaScript can detect a button click and then change text on the page without reloading the entire page.
Important Point
The JavaScript language itself provides the core programming features. The browser provides additional Web APIs that allow JavaScript to interact with the web page and browser environment.
Summary
JavaScript code is loaded by the browser and processed by a JavaScript engine. The engine processes and executes the code, while the browser provides additional APIs for interacting with the web page and browser environment.