JavaScript Guide

JavaScript - Run and Understand

A student guide to JavaScript, the programming language of the web: 121 topics in 24 chapters, from variables to DOM, events, async/await, mini projects, your class programs (popup boxes, form validation, calculator) and AngularJS, plus a complete function reference with 437 built-in functions (Chapter 24). Every topic has a Hindi summary, an explanation, key points, Notes, the code, a live Output and a Console. Topics made from your notes also list the corrections made to the code.

🎓 NIELIT O Level (M2-R5) ready: the guide covers every chapter of your O Level JavaScript Notes. See the O Level syllabus map, the green 🎯 O Level exam tip boxes inside the topics, the exam programs in Chapter 22 and the O Level Exam Corner (Chapter 23: exam guide, differences, common mistakes, important questions and 35 MCQs with score).

ButtonWhat it does
OutputShows the page result (for HTML examples) and the Console (console.log output and errors)
View CodeShows the full HTML + JavaScript (read only, colored)
EditLets you change the code. Ctrl+Enter also runs it.
▶ RunRuns your code again and shows the new Output and Console
Mobile / Tablet / DesktopChanges the Output width (for examples with a page)
Reset / Copy / DownloadOriginal code back / copy it / save it as an .html file
▶ PlaygroundOpens a scratchpad where you can write and run any JavaScript. In Chapter 24, Try opens a function in the Playground.

Chapters

Study tips for students

  1. Read the Notes, look at the Console output, then open Edit.
  2. Change one value (a number, a name, a condition) and press Run. Learn by trying and by making mistakes - read the red error messages.
  3. In a real browser press F12 (or right-click > Inspect) and open the Console tab. You can type JavaScript there directly.
  4. After each chapter, build something small without looking at the code. Chapter 19 has project ideas.
  5. In Chapters 20 and 21 (your class programs), read the red Corrections box - these are the most common mistakes students make.
  6. For the O Level exam: follow the syllabus map chapter by chapter, read every green exam tip, write the Chapter 22 programs by hand, then test yourself with the MCQ quiz in Chapter 23.

Works offline, AngularJS included (except the online fetch() demo). Your edits are not saved after you reload - use Download to keep your file. Code with an endless loop will freeze the page - reload to fix it.

🎓 O Level syllabus map (M2-R5: JavaScript and AngularJS)

आपके O Level नोट्स का हर अध्याय यहाँ है - टॉपिक पर क्लिक करें और कोड चलाकर सीखें।

Each row is one chapter of your NIELIT O Level JavaScript Notes. Click a topic to jump to it.

Notes chapterWhat it coversStudy it here