JavaScript Cheat Sheet 2026

The 30 highest-yield JavaScript facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. What does `Object.defineProperty()` allow you to do? → Define or modify a property with precise control over its descriptor attributes
2. What is the value of continuing education in closures and scope for JavaScript professionals? → It keeps professionals current with evolving standards and practices
3. What is the value of continuing education in es6+ features for JavaScript professionals? → It keeps professionals current with evolving standards and practices
4. What types of errors can be thrown in JavaScript? → Any value including strings, numbers, and objects
5. What happens when you use the spread operator `...` to copy an object? → A new object is created with a shallow copy of the original's own enumerable properties
6. What does `String.prototype.slice()` do with negative arguments? → Negative values count from the end of the string
7. What role does collaboration play in dom manipulation for JavaScript professionals? → It enhances outcomes through diverse perspectives and shared expertise
8. Which of the following objects has the URL property? → Document
9. When `String.prototype.match()` is called with a regex that has the `g` flag, what does it return? → An array containing all matched substrings
10. What is the value of continuing education in modules for JavaScript professionals? → It keeps professionals current with evolving standards and practices
11. What is 'lexical scope' in JavaScript? → Scope determined at author time based on where functions are written in the code
12. What does `Array.prototype.copyWithin()` do? → Copies a part of the array to another location within the same array
13. What is the value of continuing education in dom manipulation for JavaScript professionals? → It keeps professionals current with evolving standards and practices
14. What is the purpose of `Object.getPrototypeOf()`? → Returns the prototype (internal `[[Prototype]]`) of the specified object
15. What does the WebSocket attribute Socket.readyState with a value of 2 mean? → Handshake connection
16. What does `str.split(/,\s*/)` do? → Splits the string on each comma, discarding any spaces that immediately follow it
17. What is the primary benefit of version control in async programming for JavaScript? → It tracks changes and enables collaboration
18. What function was used to remove all name event handlers? → removeAllListeners(name)
19. An event emitter is which of the following? → process
20. What does `^` mean when placed at the very start of a regex pattern (outside a character class)? → Asserts the match must start at the beginning of the string
21. What is a positive lookahead assertion in a regular expression? → A zero-width assertion that matches a position only if a specified pattern follows it
22. What does the character class `[^abc]` match? → Any single character that is NOT a, b, or c
23. Which standard construct for data validation is available in the development environment? → All of the above
24. What does `String.prototype.includes()` do? → Returns true if the string contains the given substring, otherwise false
25. Which professional attribute is most valued in modules within the JavaScript field? → Accountability and commitment to standards
26. What does the quantifier `{2,5}` mean in a regular expression? → Matches between 2 and 5 occurrences of the preceding token
27. What is the value of continuing education in node.js basics for JavaScript professionals? → It keeps professionals current with evolving standards and practices
28. What does `Object.keys()` return? → An array of an object's own enumerable property names
29. What does `Promise.race()` return? → A promise that resolves or rejects with the value of the first settled promise
30. What does the `y` (sticky) flag do in a JavaScript regular expression? → Forces the match to start exactly at the regex's lastIndex position