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| Section | Weight | Objectives |
|---|---|---|
| Topic 1: Asynchronous Programming | 13% | - Callbacks, promises, async/await - Event loop and execution flow |
| Topic 2: Objects, Functions, and Classes | 25% | - ES6 classes, inheritance, modules, decorators - Object creation, properties, prototypes - Function types, scope, closures, arrow functions |
| Topic 3: Testing | 7% | - Test coverage and improvement - Unit test structure and effectiveness |
| Topic 4: Server Side JavaScript | 8% | - Package management and CLI tools - Node.js fundamentals and core modules |
| Topic 5: Variables, Types, and Collections | 23% | - Data types, type coercion, truthy/falsy values - JSON parsing and manipulation - Strings, numbers, dates, arrays and methods - Variable declaration and scope |
| Topic 6: Debugging and Error Handling | 7% | - Error types and handling strategies - Console usage, breakpoints and debugging techniques |
| Topic 7: Browser and Events | 17% | - Browser APIs and developer tools - DOM selection and manipulation - Event handling, propagation, listeners |
>> JS-Dev-101 Exam Exercise <<
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NEW QUESTION # 140
Given a value, which three options can a developer use to detect if the value is NaN?
Answer: B,C,E
Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript knowledge:
In JavaScript, NaN has some special properties:
NaN is not equal to anything, including itself.
Equality operators (==, ===) do not work for detecting NaN.
Check each option:
A . value === Number.NaN
Number.NaN is just NaN.
But NaN === NaN is always false.
So this expression is never true and cannot be used to detect NaN.
B . value == NaN
Same issue. NaN == NaN is always false.
So this also never detects NaN.
C . Object.is(value, NaN)
Object.is is a more precise equality comparison method.
It treats NaN as equal to NaN: Object.is(NaN, NaN) is true.
So Object.is(value, NaN) is a valid way to detect NaN.
D . value !== value
Because NaN is the only JavaScript value that is not equal to itself,
value !== value is true only when value is NaN.
This is a classic trick for NaN detection.
E . Number.isNaN(value)
Number.isNaN is the recommended modern way to check if a value is NaN without coercion.
It returns true only if value is actually the number NaN.
Therefore, the three correct ways are:
Object.is(value, NaN)
value !== value
Number.isNaN(value)
________________________________________
NEW QUESTION # 141
Given the code below:
01 const delay = async delay => {
02 return new Promise((resolve, reject) => {
03 console.log(1);
04 setTimeout(resolve, delay);
05 });
06 };
07
08 const callDelay = async () => {
09 console.log(2);
10 const yup = await delay(1000);
11 console.log(3);
12 };
13
14 console.log(4);
15 callDelay();
16 console.log(5);
What is logged to the console?
Answer: A
Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge:
Execution order:
Top-level code runs synchronously:
Line 14: console.log(4); → logs 4.
Line 15: callDelay(); is called.
Inside callDelay:
Line 9: console.log(2); → logs 2.
Line 10: await delay(1000);:
Calls delay(1000).
Inside delay(1000):
Line 3: console.log(1); → logs 1.
Line 4: setTimeout(resolve, delay); schedules resolve in 1000 ms.
delay returns a pending Promise. await pauses callDelay here and returns control to the event loop.
Back to top-level:
Line 16: console.log(5); → logs 5.
So synchronous log sequence is: 4, 2, 1, 5.
After ~1000 ms:
The setTimeout in delay resolves the Promise.
The await in callDelay resumes.
Line 11: console.log(3); → logs 3.
Final log order: 4 2 1 5 3.
Both A and B show the same sequence; one must be chosen, so A is correct.
Concepts: async/await flow, Promise resolution timing, event loop, and ordering of synchronous vs timer callbacks.
________________________________________
NEW QUESTION # 142
A developer imports:
import printPrice from '/path/PricePrettyPrint.js';
What must be true about printPrice for this import to work?
Answer: A
Explanation:
________________________________________
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge The syntax:
import printPrice from 'module';
means the module must export its function as a default export:
export default function printPrice() { ... }
Why the others are wrong:
Named exports require curly braces:
import { printPrice } from 'module';
"all export" and "multi export" are not JavaScript terms.
Therefore, printPrice must be the default export.
________________________________________
JavaScript Knowledge Reference (text-only)
Default imports use: import name from 'module'.
Named imports require braces: import { name } from 'module'.
NEW QUESTION # 143
A page loads 50+ <div class="ad-library-item"> elements, all ads.
Developer wants to quickly and temporarily remove them.
Options:
Answer: A
Explanation:
________________________________________
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge The goal:
"Temporarily and quickly remove them."
The fastest way is to run a script in the browser console that removes all such elements:
document.querySelectorAll('.ad-library-item').forEach(el => el.remove()); This immediately removes all 50+ elements and requires no page reload.
Option analysis:
A & B: Preventing load events is unreliable and does not remove already-created DOM nodes.
C: Correct-console code can remove all matching DOM elements instantly.
D: Possible but extremely slow; removing 50+ elements one by one in the inspector is not "quick." Therefore, C is the best answer.
________________________________________
JavaScript Knowledge Reference (text-only)
The browser console can run arbitrary JavaScript that manipulates the DOM.
document.querySelectorAll() returns all matching DOM nodes.
Nodes can be removed using .remove().
NEW QUESTION # 144
A developer wrote the following code to test a sum3 function that takes in an array of numbers and returns the sum of the first three numbers in the array. The test passes:
01 let res = sum3([1, 2, 3]);
02 console.assert(res === 6);
03
04 res = sum3([1, 2, 3, 4]);
05 console.assert(res === 6);
A different developer made changes to the behavior of sum3 to instead sum all of the numbers present in the array.
Which two results occur when running the test on the updated sum3 function?
Answer: C,D
Explanation:
New behavior: sum3 now returns the sum of all elements.
Line 01: sum3([1, 2, 3]) → 1 + 2 + 3 = 6
Assertion on line 02: res === 6 → passes.
Line 04: sum3([1, 2, 3, 4]) → 1 + 2 + 3 + 4 = 10
Assertion on line 05: res === 6 → 10 === 6 is false, so the assertion fails.
So:
Line 02 assertion passes → D.
Line 05 assertion fails → C.
________________________________________
NEW QUESTION # 145
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