How Web Browsers Interpret the Stack, then JavaScript and Its Flavors

HTML Parsing → DOM

The HTML stream is tokenized into elements and attributes. The DOM tree is built to represent the document’s structure and content.

CSS Parsing → CSSOM

CSS rules are parsed into an object model. Cascading rules, inheritance, and specificity determine the final style applied to each element.

Render Tree, Layout, and Paint

The render tree combines the DOM and CSSOM. Layout determines the position and size of each node, then the browser paints pixels to the screen.

JavaScript Execution

Browsers implement the ECMAScript standard, exposing APIs that allow scripts to manipulate the DOM, handle events, and perform network operations.

Language vs. Platform

• ECMAScript: Defines syntax, types, and core language features.
• Web APIs: Expose the DOM, Fetch, Storage, and Workers.

Modules

Use ES modules with <script type="module"> and the import/export syntax to structure code and manage dependencies.

Common Patterns

• Progressive enhancement for static content.
• Component-based design for complex UIs.
• TypeScript for large-scale maintainability.

TypeScript

Adds static typing to JavaScript. Compiles to standard JavaScript for runtime execution.

function greet(name: string): string {
  return `Hello, ${name}`;
}
console.log(greet("Ada"));

React + JSX

JSX is a syntax extension that compiles to function calls returning virtual DOM elements.

export default function App() {
  return <button onClick={() => alert('Hi')}>Click</button>;
}

Vue

A framework emphasizing reactivity and templates.

<script setup>
import { ref } from 'vue'
const count = ref(0)
</script>

<template>
  <button @click="count++">Clicked {{ count }}</button>
</template>

Svelte

A compiler that turns declarative components into efficient vanilla JavaScript code.

<script> let n = 0; </script>
<button on:click={() => n++}>Clicked {n}</button>

Angular

A full-featured framework using TypeScript, templates, and dependency injection for enterprise-grade applications.

import { Component } from '@angular/core';
@Component({
  selector: 'hello',
  template: `<button (click)="onClick()">Click</button>`
})
export class HelloComponent {
  onClick() { alert('Hi'); }
}

Modules and Bundling

• ES Modules: Supported natively in browsers.
• Bundlers: Tools like Vite, esbuild, and Webpack optimize code.
• Transpilers: Convert modern syntax (TypeScript, JSX) into supported JavaScript.

Choosing an Approach

• Simple static sites: vanilla JavaScript.
• Interactive interfaces: React or Vue.
• Large projects: TypeScript with Angular or React.
• Performance-critical: Svelte or lighter alternatives.

Performance Practices

• Load critical CSS first; defer nonessential scripts.
• Batch DOM reads and writes to avoid reflows.
• Use browser dev tools to measure rendering and optimize hot paths.