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Salesforce JS-Dev-101 Prüfungsplan:

ThemaEinzelheiten
Thema 1
  • Browser and Events: Covers DOM manipulation, event handling and propagation, browser-specific APIs, and using Browser Developer Tools to inspect code behavior.
Thema 2
  • Testing: Covers evaluating unit test effectiveness against a block of code and modifying tests to improve their coverage and reliability.
Thema 3
  • Debugging and Error Handling: Covers proper error handling techniques and the use of the console and breakpoints to debug code.
Thema 4
  • Objects, Functions, and Classes: Covers function, object, and class implementations to meet business requirements, along with the use of modules, decorators, variable scope, and execution flow.
Thema 5
  • 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.
Thema 6
  • Server Side JavaScript: Covers Node.js implementations, CLI commands, core modules, and package management solutions for given scenarios.

>> JS-Dev-101 Testengine <<

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Salesforce Certified JavaScript Developer - Multiple Choice JS-Dev-101 Prüfungsfragen mit Lösungen (Q117-Q122):

117. Frage
Refer to the HTML below:
<div id="main">
<ul>
<li>Leo</li>
<li>Tony</li>
<li>Tiger</li>
</ul>
</div>
Which JavaScript statement results in changing " Tony" to "Mr. T."?

Antwort: B


118. Frage
A team at Universal Containers works on a big project and uses yarn to manage the project's dependencies.
A developer added a dependency to manipulate dates and pushed the updates to the remote repository. The rest of the team complains that the dependency does not get downloaded when they execute yarn.
What could be the reason for this?

Antwort: D

Begründung:
In JavaScript server-side development using Node.js, dependency management is typically handled through package managers such as npm or yarn. These tools categorize installed packages into:
dependencies - required for running the application in any environment
devDependencies - required only during development (testing tools, build tools, documentation generators, etc.) When a package is installed using:
yarn add <package> --dev
it is placed under the "devDependencies" section of package.json.
Behavior of Production Mode
Node.js uses the environment variable:
NODE_ENV=production
When this environment variable is set to production, both npm and Yarn follow the standard Node.js convention and skip installing devDependencies. This is done to optimize production builds and reduce deployment size. This is a known and documented behavior in Node.js package management tools.
Therefore, if:
The developer added the date-manipulation library as a dev dependency, and Other team members execute yarn in an environment where NODE_ENV=production is set, then Yarn will not install that dependency because devDependencies are intentionally excluded in production mode.
This explains the behavior described in the question.
Why the Other Options Are Incorrect
Option A:
"YARN_ENV is set to production" is incorrect because Yarn does not use the variable YARN_ENV for dependency installation behavior. Node.js tools use NODE_ENV, not YARN_ENV.
Option B:
This is incorrect because Yarn automatically writes dependencies into package.json. Unlike older npm versions, there is no need for the --save flag.
Option D:
There is no such option as --add. The correct syntax is simply:
yarn add <package>
Missing an option that does not exist cannot be the cause.
JavaScript Knowledge Reference
Node.js uses the environment variable NODE_ENV to determine production or development mode.
Package managers (npm and Yarn) follow the rule that when NODE_ENV=production, only "dependencies" are installed and "devDependencies" are skipped.
Yarn automatically persists installed packages to package.json without requiring --save.
Yarn uses the command yarn add to add dependencies; there is no --add flag.


119. Frage
Refer to the code below:
01 async function functionUnderTest(isOK) {
02 if (isOK) return 'OK';
03 throw new Error('not OK');
04 }
Which assertion accurately tests the above code?

Antwort: C

Begründung:
Comprehensive and Detailed Explanation From Exact Extract JavaScript knowledge:
The function:
async function functionUnderTest(isOK) {
if (isOK) return 'OK';
throw new Error('not OK');
}
Behavior:
If isOK is true:
The function resolves (fulfills the promise) with value 'OK'.
If isOK is false:
The function throws, which in an async function becomes a rejected promise with Error('not OK').
We want an assertion that accurately tests the successful path for isOK === true.
Key points about console.assert:
Signature: console.assert(condition, message?)
If condition is falsy, it logs message as an assertion failure.
If condition is truthy, nothing is logged.
We also must understand await:
await functionUnderTest(true) will resolve to the string 'OK'.
Now evaluate options.
Option A:
console.assert(await functionUnderTest(true), 'OK');
await functionUnderTest(true) → 'OK' (truthy).
console.assert('OK', 'OK');
Condition is 'OK' (truthy), so assertion passes.
The message 'OK' is only shown if the condition is falsy, which it is not.
This correctly verifies that the promise resolved (i.e., did not reject). Among the given options, this is the only one that both:
Uses await properly on the async function, and
Associates the message with the expected success "OK".
Option B:
console.assert(await (functionUnderTest(true), 'not OK'));
Inside the parentheses, the comma operator (a, b) evaluates a, discards it, and returns b.
So (functionUnderTest(true), 'not OK'):
Calls functionUnderTest(true) (returns a promise, but its result is discarded), The expression evaluates to the string 'not OK'.
Then await 'not OK' just resolves to 'not OK' immediately (not a promise).
console.assert('not OK');
Condition is 'not OK' (truthy), so the assertion passes regardless of what functionUnderTest actually does.
This does not meaningfully test the function and is misleading.
Option C:
console.assert(functionUnderTest(true), 'OK');
functionUnderTest(true) returns a Promise, not the string 'OK' directly.
A Promise object is always truthy.
So console.assert(promise, 'OK') will pass, even if the promise later rejects.
Also, there is no await, so we are not actually waiting for the async result.
This is not a correct way to assert on an async function's resolved value.
Option D:
console.assert(await functionUnderTest(true), 'not OK');
await functionUnderTest(true) still resolves to 'OK' (truthy).
console.assert('OK', 'not OK'); passes.
However, the message 'not OK' is the opposite of what we expect for the success case and is only used when the condition fails.
This makes the assertion logically inconsistent with the function behavior (it would show "not OK" if the assertion failed).
Therefore, the only assertion that:
Properly waits on the async function, and
Has expectation text that matches the successful behavior ('OK')
is:
Study Guide / Concept Reference (no links):
async and await behavior in JavaScript
Promises resolving vs rejecting in async functions
console.assert(condition, message) usage
Truthy and falsy values in JavaScript
Comma operator (a, b) semantics
________________________________________


120. Frage
Given the code below:
01 setTimeout(() => {
02 console.log(1);
03 }, 1100);
04 console.log(2);
05 new Promise((resolve, reject) => {
06 setTimeout(() => {
07 reject(console.log(3));
08 }, 1000);
09 }).catch(() => {
10 console.log(4);
11 });
12 console.log(5);
What is logged to the console?

Antwort: B

Begründung:
Comprehensive and Detailed Explanation From JavaScript Knowledge:
We must track synchronous code, setTimeout callbacks (macrotasks), and Promise rejection handling (microtasks).
Step-by-step:
Synchronous code first:
Line 01-03: Schedules a timeout at 1100 ms: logs 1 (later).
Line 04: console.log(2); → logs 2.
Lines 05-09: Construct a new Promise.
The executor runs immediately.
Inside it, another setTimeout is set for 1000 ms:
setTimeout(() => {
reject(console.log(3));
}, 1000);
Line 09-11: .catch(() => { console.log(4); }) attached to the promise.
Line 12: console.log(5); → logs 5.
So after all synchronous code, the console has:
2
5
At 1000 ms: inner setTimeout fires
The callback:
() => {
reject(console.log(3));
}
Inside:
console.log(3) runs first, logging 3.
console.log(3) returns undefined.
Then reject(undefined) is called.
So at about 1000 ms, we log:
3
When the promise is rejected:
The .catch handler is scheduled as a microtask.
After the current macrotask (the timeout callback) completes, the microtask queue runs.
Thus .catch(() => { console.log(4); }) runs shortly after, in the same 1000 ms tick.
So immediately after 3, the catch handler logs:
4
Now the logs in order are:
2
5
3
4
At 1100 ms: outer setTimeout fires
The callback from line 01 runs:
console.log(1);
Logs: 1.
Final log order:
2 (line 4, sync)
5 (line 12, sync)
3 (1000 ms timeout, then inside logs before reject)
4 (promise catch microtask after rejection)
1 (1100 ms timeout)
Concatenated: 25341.
Therefore, the correct option is:
Study Guide / Concept Reference (no links):
Event loop: call stack, macrotask queue (timers), microtask queue (promises) setTimeout scheduling and ordering Promise rejection, .catch, and microtasks Evaluation order of function arguments (reject(console.log(3)))
________________________________________


121. Frage
Given the following code:
let x = null;
console.log(typeof x);
What is the output?

Antwort: B


122. Frage
......

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