Definition
Core JavaScript concepts for browser scripting: variables, data types, operators, control flow, functions, scope, and event handling—the behavioral layer that adds interactivity on top of HTML structure and CSS presentation.
Why It Matters
The web is the world’s most accessible operating system. Mastering JavaScript is not just about “coding”; it’s about owning the logic layer of the modern world, turning static information into interactive, functional power.
Core Concepts
- Client-Side: Runs in the browser, not the server.
- Variables:
var(function-scoped), strings, numbers, booleans, arrays, null, undefined. - Strict Equality:
===checks value and type;==allows coercion. - Control Flow:
if/else,forloops, functions with parameters and return values. - Scope: Global (outside functions) vs local (inside functions with
var). - Events:
onclick,onload,addEventListener()for click, load, submit, hover.
// Variable declaration and event handling
const button = document.querySelector('button');
button.addEventListener('click', () => {
let message = 'Hello, World!';
console.log(message);
});