JS-Dev-101 Practice Exam | JS-Dev-101 Reliable Test Questions

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Salesforce JS-Dev-101 Exam Syllabus Topics:

Topic	Details
Topic 1	Server Side JavaScript: Covers Node.js implementations, CLI commands, core modules, and package management solutions for given scenarios.
Topic 2	Browser and Events: Covers DOM manipulation, event handling and propagation, browser-specific APIs, and using Browser Developer Tools to inspect code behavior.
Topic 3	Variables, Types, and Collections: Covers declaring and initializing variables, working with strings, numbers, dates, arrays, and JSON, along with understanding type coercion and truthy falsy evaluations.
Topic 4	Debugging and Error Handling: Covers proper error handling techniques and the use of the console and breakpoints to debug code.
Topic 5	Asynchronous Programming: Covers asynchronous programming concepts and understanding how the event loop controls execution flow and determines outcomes.

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JS-Dev-101 Quiz Torrent: Salesforce Certified JavaScript Developer - Multiple Choice - JS-Dev-101 Exam Guide & JS-Dev-101 Test Bootcamp

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Salesforce Certified JavaScript Developer - Multiple Choice Sample Questions (Q100-Q105):

NEW QUESTION # 100
A Node.js server library uses events and callbacks. The developer wants to log any issues the server has at boot time.
Which code logs an error with an event?

A. try {
server.start();
} catch(error) {
B. server.on('error', (error) => {
console.log('ERROR', error);
});
C. server.catch('error) => {
console.log('ERROR', error);
});
D. server.error('error) => {
console.log('ERROR', error);
});

Answer: B

Explanation:
console.log('ERROR', error);
}
Explanation:
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.

NEW QUESTION # 101
A developer is debugging a web server that uses Node.js The server hits a runtimeerror every third request to an important endpoint on the web server.
The developer added a break point to the start script, that is at index.js at he root of the server's source code. The developer wants to make use of chrome DevTools to debug.
Which command can be run to access DevTools and make sure the breakdown is hit ?

A. Node --inspect index.js
B. Node --inspect-brk index.js
C. node -i index.js
D. Node inspect index.js

Answer: A

NEW QUESTION # 102
Function to test:
01 const sum3 = (arr) => {
02 if (!arr.length) return 0;
03 if (arr.length === 1) return arr[0];
04 if (arr.length === 2) return arr[0] + arr[1];
05 return arr[0] + arr[1] + arr[2];
06 };
Which two assert statements are valid tests for this function?

A. console.assert(sum3([-3, 2]) === -1);
B. sum3([0])
C. console.assert(sum3([1, '2']) == 12);
D. console.assert(sum3([0]) === 0);
E. console.assert(sum3(['hello', 2, 3, 4]) === NaN);

Answer: A,D

Explanation:
Length 1 → returns arr[0] → 0.
Assertion: 0 === 0 → true.
Also a correct and meaningful test.
Therefore, the valid and logically correct tests here are C and D.
Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge:
Evaluate each test:
A). sum3([1, '2'])
Array length is 2 → line 4: arr[0] + arr[1] → 1 + '2' → '12' (string).
Assertion: '12' == 12 is true (type coercion).
However, this "test" is not logically correct: a numeric sum function should not be expected to return '12' as a string. It passes only because of weak equality coercion, so it is not a good/valid test of correct behavior.
B). sum3(['hello', 2, 3, 4])
Length ≥ 3 → line 5: 'hello' + 2 + 3 → 'hello2' + 3 → 'hello23'.
'hello23' === NaN is always false because NaN is never equal to anything, not even itself.
This assertion fails and also misunderstands how NaN comparisons work.
C). sum3([-3, 2])
Length 2 → -3 + 2 = -1.
Assertion: -1 === -1 → true.
This is a correct and meaningful test.

NEW QUESTION # 103
Refer to the code:
01 const exec = (item, delay) =>
02 new Promise(resolve => setTimeout(() => resolve(item), delay));
03
04 async function runParallel() {
05 const [result1, result2, result3] = await Promise.all(
06 [exec('x', '100'), exec('y', '500'), exec('z', '100')]
07 );
08 return `parallel is done: ${result1}${result2}${result3}`;
09 }
Which two statements correctly execute runParallel()?

A. runParallel().then(data);
B. runParallel().then(function(data){
return data;
});
C. runParallel().done(function(data){
return data;
});
D. async runParallel().then(data);

Answer: A,B

Explanation:
Facts about JavaScript Promises:
runParallel() is declared async, which means it always returns a Promise.
Promises are consumed using .then(), .catch(), and .finally().
There is no .done() method in native JavaScript Promises.
The async keyword cannot be placed before a function call (option A is invalid syntax).
Analysis of each option:
A . async runParallel().then(data);
Invalid syntax. async cannot prefix an expression.
B . Valid. Calls the function and attaches a .then() handler.
C . Invalid. .done() is not part of JavaScript Promise API.
D . Valid. Calls runParallel() and chains .then().
Therefore the correct answers are B and D.
JavaScript Knowledge Reference (text-only)
async functions return Promises.
Promises use .then() to retrieve resolved values.
.done() is not part of the standard Promise interface.

NEW QUESTION # 104
Given:
const str = 'Salesforce';
Which two statements result in 'Sales'?

A. str.substr(0, 5);
B. str.substring(1, 5);
C. str.substring(0, 5);
D. str.substr(1, 5);

Answer: A,C

Explanation:
str = 'Salesforce'
Index positions:
S(0) a(1) l(2) e(3) s(4) f(5) o(6) r(7) c(8) e(9)
substring(start, end)
Start index inclusive, end index exclusive.
str.substring(0, 5) → characters at indices 0-4 → "Sales"
str.substring(1, 5) → indices 1-4 → "ales"
substr(start, length)
Start index, then number of characters.
str.substr(0, 5) → 5 characters starting at index 0 → "Sales"
str.substr(1, 5) → 5 characters from index 1 → "alesf"
So the expressions that return "Sales" are A and C.

NEW QUESTION # 105
......

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