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Study and Certification Guide
Question 1. Which of the following best describes the primary role of JavaScript in the Web Triad? A) Define the page layout and visual style B) Store data on the server C) Provide interactivity and behavior to web pages D) Deliver multimedia content Answer: C Explanation: In the Web Triad, JavaScript is responsible for adding dynamic behavior and interactivity, while HTML provides structure and CSS handles presentation. Question 2. Which ECMAScript version introduced the let and const keywords? A) ES B) ES C) ES6 (ES2015) D) ES7 (ES2016) Answer: C Explanation: ES6 added block‑scoped variable declarations with let and immutable bindings with const, improving on the function‑scoped var. Question 3. What will the expression typeof NaN return? A) "number" B) "NaN" C) "undefined" D) "object" Answer: A
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Explanation: NaN (Not‑a‑Number) is a special numeric value; typeof NaN evaluates to "number". Question 4. Which operator should be used to compare both value and type in JavaScript? A) = B) == C) === D) != Answer: C Explanation: The strict equality operator === checks that both the value and the data type are identical. Question 5. In a for loop, which part is executed first? A) Increment expression B) Condition test C) Initialization statement D) Loop body Answer: C Explanation: The initialization runs once before the loop starts, then the condition is evaluated before each iteration. Question 6. Which of the following is a correct function expression? A) function foo() {} B) var foo = function() {}; C) function = foo() {}; D) var foo();
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A) querySelectorAll() B) getElementsByClassName() C) getElementById() D) getElementsByTagName() Answer: B Explanation: getElementsByClassName() returns a live collection that updates when the DOM changes. Question 10. To prevent a form from submitting, which method should be called inside an event handler? A) event.stopPropagation() B) event.preventDefault() C) event.cancel() D) event.stop() Answer: B Explanation: preventDefault() stops the default action (form submission) while allowing other code to run. Question 11. Which of the following statements about null is correct? A) It is a type of object. B) It is the same as undefined. C) It indicates the intentional absence of any object value. D) It can be used as a numeric operator. Answer: C Explanation: null is a primitive that explicitly represents “no value” or “empty object reference”.
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Question 12. What will console.log(typeof typeof 42); output? A) "number" B) "string" C) "undefined" D) "object" Answer: B Explanation: typeof 42 yields "number" (a string). Applying typeof again to that string returns "string". Question 13. Which statement correctly creates a constant that cannot be reassigned? A) const PI = 3.14; B) let const PI = 3.14; C) var PI = const 3.14; D) constant PI = 3.14; Answer: A Explanation: The const keyword declares a block‑scoped constant; its value cannot be changed after initialization. Question 14. In JavaScript, which method is used to parse a JSON string into an object? A) JSON.stringify() B) JSON.parse() C) JSON.decode() D) JSON.toObject() Answer: B
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Answer: B Explanation: classList.add() appends a class without overwriting existing classes. Question 18. Which loop guarantees that its body will execute at least once? A) for B) while C) do...while D) forEach Answer: C Explanation: The do...while loop checks its condition after executing the body, ensuring one execution. Question 19. What is the result of Math.max(5, 9, 2, 7)? A) 2 B) 5 C) 7 D) 9 Answer: D Explanation: Math.max() returns the largest numeric argument; here it is 9. Question 20. Which of the following statements about hoisting is true? A) Only let and const declarations are hoisted. B) Function declarations are hoisted, but function expressions are not. C) Variable assignments are hoisted, but declarations are not. D) Hoisting only occurs in strict mode.
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Answer: B Explanation: Function declarations are moved to the top of their scope during compilation, while function expressions behave like normal variable assignments. Question 21. In an event listener, what does the this keyword refer to? A) The global window object. B) The element on which the listener is attached. C) The event object. D) The parent node of the element. Answer: B Explanation: Within a standard event handler, this points to the element that received the event. Question 22. Which method would you use to stop the propagation of an event to parent elements? A) event.stopPropagation() B) event.preventDefault() C) event.cancelBubble() D) event.stopImmediatePropagation() Answer: A Explanation: stopPropagation() prevents further bubbling of the event up the DOM tree. **Question 23. What will the following code output?
let a = [1,2,3]; let b = a; ## Study and Certification Guide Answer: A Explanation: `setTimeout` returns a numeric timer identifier that can be used with `clearTimeout`. **Question 26. Which of the following statements about the `Date` object is correct?** A) `new Date()` returns the current date and time in UTC. B) `Date.now()` returns a Date object. C) `Date.parse('2023- 01 - 01')` returns the number of milliseconds since 1 Jan 1970. D) `Date.getDay()` is a static method. Answer: C Explanation: `Date.parse()` converts a date string into a timestamp (milliseconds since the epoch). `new Date()` returns a Date object in local time, and `Date.now()` returns a timestamp, not an object. **Question 27. Which of the following is the correct way to add an inline click handler to a button element using JavaScript?** A) `button.onclick = function(){ alert('Clicked'); };` B) `button.addEventListener('click', alert('Clicked'));` C) `button.on('click', function(){ alert('Clicked'); });` D) `button.attachEvent('onclick', function(){ alert('Clicked'); });` Answer: A Explanation: Assigning a function to the `onclick` property sets an inline handler. Option B incorrectly invokes `alert` immediately. **Question 28. Which of the following statements will correctly remove the element with id `item` from the DOM?** A) `document.getElementById('item').remove();` ## Study and Certification Guide B) `document.removeChild('item');` C) `document.getElementById('item').delete();` D) `document.body.removeChild('item');` Answer: A Explanation: The `remove()` method on a node detaches it from its parent. Option D attempts to remove a string, not a node. **Question 29. In JavaScript, which keyword creates a private variable inside a constructor function?** A) `private` B) `var` C) `let` D) `const` Answer: B Explanation: Variables declared with `var` inside a constructor are scoped to that function and not accessible outside, effectively private. **Question 30. Which method converts an array-like object (e.g., `NodeList`) into a true array?** A) `Array.from()` B) `Array.toArray()` C) `Array.cast()` D) `Array.slice()` Answer: A Explanation: `Array.from()` creates a new array from an iterable or array‑like object. ## Study and Certification Guide **Question 34. Which method is used to asynchronously fetch JSON data from a server in modern JavaScript?** A) `XMLHttpRequest` B) `fetch()` C) `ajax()` D) `getJSON()` Answer: B Explanation: The `fetch` API returns a Promise and is the modern way to request resources, often followed by `.json()`. **Question 35. Which statement correctly creates a self‑invoking anonymous function?** A) `function(){ /*...*/ }();` B) `(function(){ /*...*/ })();` C) `(() => { /*...*/ })();` D) Both B and C Answer: D Explanation: Wrapping the function in parentheses creates a function expression that can be immediately invoked; both classic and arrow syntax work. **Question 36. Which of the following is a correct way to clone an object shallowly?** A) `let copy = Object.clone(original);` B) `let copy = {...original};` C) `let copy = original.slice();` D) `let copy = original.copy();` Answer: B ## Study and Certification Guide Explanation: The spread operator creates a shallow copy of an object's own enumerable properties. **Question 37. What does the `debugger;` statement do when executed?** A) Logs a message to the console. B) Throws a runtime error. C) Pauses execution if a debugging tool is attached. D) Removes all breakpoints. Answer: C Explanation: `debugger;` triggers a breakpoint in browsers that have developer tools open. **Question 38. Which of the following is the correct syntax to add an event listener for the `submit` event on a form with id `myForm`?** A) `document.getElementById('myForm').addEventListener('submit', handleSubmit);` B) `document.getElementById('myForm').on('submit', handleSubmit);` C) `document.getElementById('myForm').attachEvent('onsubmit', handleSubmit);` D) `document.getElementById('myForm').listen('submit', handleSubmit);` Answer: A Explanation: `addEventListener` is the standard method for registering event handlers. **Question 39. Which of the following statements about arrow functions is FALSE?** A) Arrow functions do not have their own `this`. B) Arrow functions can be used as constructors with `new`. C) Arrow functions inherit `arguments` from the surrounding scope. D) Arrow functions have an implicit return when written without braces. Answer: B ## Study and Certification Guide ## B) ```js function debounce(){ setTimeout(search,300); }
C)
let timer = setTimeout(search,300); function debounce(){ clearTimeout(timer); }
D) None of the above. Answer: A Explanation: Debouncing requires clearing any existing timer before setting a new one, ensuring the function runs only after inactivity. Question 42. Which method returns a new array containing only the elements that pass a test implemented by a provided function? A) filter() B) map() C) reduce() D) some() Answer: A Explanation: filter creates a new array with elements for which the callback returns a truthy value. Question 43. In the context of the DOM, what does the term “node” refer to? A) Only element nodes (``, <p>, etc.)
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B) Any object in the DOM tree, including elements, text, and comments C) Only the root document node D) Only attribute nodes Answer: B Explanation: A node can be an element, text, comment, document, or attribute; it is any object in the DOM hierarchy. **Question 44. Which of the following will correctly read the value of a selected option from a element?** A) `document.getElementById('colors').value;` B) `document.getElementById('colors').selected;` C) `document.querySelector('#colors').option;` D) `document.getElementById('colors').innerHTML;` Answer: A Explanation: The `value` property of a element returns the value of the currently selected `
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B) Executes a reducer function on each element to produce a single accumulated value. C) Filters elements based on a predicate. D) Checks if at least one element satisfies a condition. Answer: B Explanation: reduce applies a callback that accumulates a result across the array, returning a single value. Question 48. Which of the following is the correct way to add a CSS rule that sets color: red to all <p> elements using JavaScript? A)
document.styleSheets[0].insertRule('p { color: red; }', 0);
B)
document.head.appendChild('');
C)
document.querySelectorAll('p').style.color = 'red';
D)
document.createElement('style').innerHTML = 'p{color:red;}';
Answer: A
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Explanation: insertRule adds a CSS rule to a stylesheet object. Option C tries to set style on a NodeList, which is invalid. Question 49. Which of the following statements about the let keyword is FALSE? A) let variables are block‑scoped. B) let declarations are hoisted to the top of their block. C) let allows redeclaration in the same scope. D) let cannot be accessed before its declaration. Answer: C Explanation: let does not permit redeclaration within the same scope; attempting to do so causes a SyntaxError. Question 50. Which of the following is a correct way to serialize an object data into a JSON string? A) JSON.stringify(data); B) data.toJSON(); C) JSON.parse(data); D) data.serialize(); Answer: A Explanation: JSON.stringify converts a JavaScript value to a JSON‑formatted string. **Question 51. What will the following code output?
console.log([] + []); ```** A) `0`
