Salesforce Developer JavaScript-Developer-I Book

Evaluate each option:

A. Arguments for .then() are optional.

This is correct.

then() has the signature:

promise.then(onFulfilled?, onRejected?)

Both arguments (onFulfilled and onRejected) are optional.

If a callback is not supplied, JavaScript provides a default pass-through handler.

B. .then() cannot be added after a catch.

Incorrect.

Promises support chaining in any order:

promise

catch(...)

then(...);

After a catch, the chain continues normally.

C. .then() manipulates and returns the original promise.

Incorrect.

then() always returns a new promise , not the original one.

This is fundamental to promise chaining behavior.

D. Returning values in .then() is not necessary.

Incorrect.

If you want the next .then() in the chain to receive a value, the current .then() must explicitly return it:

then(value = > {

return value * 2; // passes to next .then()

})

If nothing is returned, the next .then() receives undefined.

Why A is correct

It is the only statement that accurately describes built-in Promise behavior:

then() accepts optional arguments.

JavaScript Knowledge References (text-only)

.then(onFulfilled?, onRejected?) accepts optional handlers.

Promise chaining creates new promises for each .then().

catch() can be followed by additional .then() calls.

Returning inside .then() passes values to the next step in the chain.

console.log() in browser-side JavaScript writes output to the browser’s JavaScript console , which is available in the browser’s Developer Tools.

In a typical browser (Chrome, Firefox, Edge, etc.), you open DevTools and go to the Console tab.

Any console.log( " Page has loaded! " ); executed in page JavaScript will appear there.

Why A is correct:

The function onLoad is a client-side function (runs in the browser).

When it executes, the console.log call goes to the browser’s JavaScript console , not the server.

Why the others are incorrect:

B. On the terminal console running the web server

That console shows logs from the server-side runtime (e.g., Node.js logs).

This code is clearly browser-side JavaScript (no Node.js or server context shown).

Therefore, the output does not appear in the terminal.

C. In the browser performance tools log

Performance tools (Timeline, Performance tab, etc.) show metrics about rendering, CPU time, network, etc., not generic console.log messages.

console.log messages appear in the Console tab, not in performance logs.

D. On the webpage console log

There is no built-in concept of a “webpage console log” UI rendered on the page itself by default.

Unless you explicitly code something to display logs in the DOM, console.log output is not visible on the page, only in Developer Tools.

Therefore, the correct place to see that log is:

Answer: A

JavaScript knowledge / Study Guide references (concept names only, no links):

Browser Developer Tools – Console tab

console.log() in client-side JavaScript

Difference between client-side logs and server-side logs

document.querySelector( ' #row-as ' ) returns the single element with id row-as.

That element has a classList property with add, remove, etc.

Correct usage:

document.querySelector( ' #row-as ' ).classList.add( ' priority-account ' );

Why others are wrong:

A: querySelectorAll returns a NodeList, not a single element, so it does not have a classList property.

C: DOM elements do not have a classes array or push; they have classList.

D: document.getElementById( ' row-as ' ) is fine to get the element, but there is no addClass method in standard DOM; that’s a jQuery-style API, not vanilla JS.

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 References (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().