Questions
JavaScript questions
Choose a question page, learn the concept, then test your understanding with a quiz.
What Is JSONP in JavaScript? Why It Was Created and How It Works
Learn what JSONP is, why it was created, how it bypassed browser restrictions, and when to use modern alternatives like CORS.
What the Double Exclamation Mark (!!) Does in JavaScript
Learn what !! means in JavaScript, how it converts values to true or false, and when to use it with clear examples and common pitfalls.
When to Use Node.js: Choosing It for Web Applications
Learn when Node.js is a strong choice, how its event loop handles I/O, and how to compare it with PHP, Python, and Ruby for web apps.
Where to Put Script Tags in HTML: defer, async, and Body Placement
Learn where to place JavaScript script tags in HTML, how defer and async affect loading, and reliable patterns for modern web pages.
Why Browsers Enforce CORS but Postman Does Not in JavaScript
Learn why browser JavaScript gets CORS errors while Postman works, and how Same-Origin Policy affects fetch and XMLHttpRequest.
Why Some JSON Responses Start with while(1); in JavaScript
Learn why APIs prepend while(1); to JSON, how it helps prevent JSON hijacking, and what safer modern alternatives exist.
Why `++[[]][+[]] + [+[]]` Returns "10" in JavaScript
Learn why `++[[]][+[]] + [+[]]` evaluates to "10" in JavaScript by understanding coercion, unary plus, increment, and string conversion.
Why for...in Is Bad for Array Iteration in JavaScript
Learn why JavaScript for...in is unsafe for arrays, how inherited properties affect loops, and when to use for...of or array methods instead.
Writing Files in Node.js with the fs Module
Learn how to write text and JSON files in Node.js using the built-in fs module, including async, promise-based, and safe file-writing patterns.
event.preventDefault() vs return false in JavaScript and jQuery
Learn the difference between event.preventDefault() and return false in JavaScript and jQuery, including propagation, defaults, and best practices.
jQuery .prop() vs .attr(): Understanding Properties and Attributes
Learn the difference between jQuery .prop() and .attr(), when to use each, and why style, checked, and selected behave differently.
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