JS-Dev-101 Certification Exam Guide + Practice Questions

Explanation:
import * as lib from '...' imports all named exports from the module into the namespace object lib.
You then call:
lib.foo();
lib.bar();
Option D correctly imports only foo and bar, not every function. The question explicitly says “import every function… and then call foo and bar”, so A best matches.
Options B and C are invalid syntax or reference the wrong identifier.

Explanation:
In a reduce callback, you must return the new accumulator value.
Currently:
(result, current) => {
result += current;
// no return
}
This returns undefined each time, so the accumulator becomes undefined on the next iteration, leading to incorrect results.
Fix by returning result:
const sumFunction = arr => {
return arr.reduce((result, current) => {
result += current;
return result; // line 05
}, 10);
};
Option D correctly adds the return.
Options A/B/C do not fix the missing return in the reducer and therefore do not resolve the core issue.

Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge:
String: "Yay! Salesforce is amazing!"
Index positions:
'Y' at 0, 'a' at 1, 'y' at 2, '!' at 3, space at 4, 'S' at 5, 'a' at 6, 'l' at 7, 'e' at 8, 's' at 9, etc.
Substring "Sales" starts at index 5.
String.prototype.search with a regex returns the index of the first match or -1 if there is no match. searchText.search(/sales/i);
/sales/i is case-insensitive because of the i flag.
It matches "Sales" beginning at index 5.
So result1 is 5.
searchText.search(/sales/);
/sales/ is case-sensitive.
It requires lowercase "sales".
The text has "Sales" with uppercase S, so this does not match.
search returns -1 when there is no match.
So result2 is -1.
Console output:
First log: 5
Second log: -1
Option D matches this.
Concepts: regex search, case sensitivity vs i flag, String.prototype.search return values.

Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge Node.js event-based modules use the EventEmitter pattern. The correct syntax for listening to events is:
emitter.on('eventName', callback)
The server library emits an 'error' event, which must be listened to using .on.
Option analysis:
A: .catch is for Promises, not EventEmitters.
B: .error is not an EventEmitter method.
C: Correct. Listens to the 'error' event.
D: try...catch only captures synchronous errors, not event-based asynchronous errors. Therefore, the correct answer is option C.
JavaScript Knowledge Reference (text-only)
The EventEmitter API uses on(event, handler) to listen for events. Errors emitted asynchronously cannot be caught with try...catch.
The 'error' event is standard for Node.js modules to signal operational errors.

Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge A subclass created by:
Console16bit.prototype = Object.create(GameConsole.prototype); inherits all prototype methods from GameConsole, including load.
To override the inherited method, the correct syntax is to assign a new function to the method name on the prototype:
Console16bit.prototype.load = function(gamename) {
console.log(`${this.name} is loading a cartridge game: ${gamename}....`);
};
Why the other options are wrong:
A assigns something to the constructor function itself, not to the prototype method. Invalid.
B attempts to call a function in the left-hand side of an assignment; invalid syntax.
C also uses invalid syntax―prototype methods cannot be defined this way.
D is the correct definition of a prototype method override.
JavaScript Knowledge Reference (text-only)
Methods are overridden by assigning functions to Subclass.prototype.methodName.
Object.create() establishes prototype inheritance.
Constructor functions require prototype method attachment using assignment syntax.