Free TJ Practice Questions

Question 1

A notification service stores retryDelay as a nonnegative number, null, or undefined. A value of 0 deliberately disables the delay; only null and undefined should become 30.

Complete the assignment so it respects all three cases:

const delay = ______;

Accepted Answer

retryDelay ?? 30

Answer

retryDelay || 30

Answer

retryDelay && 30

Answer

retryDelay === undefined ? 30 : retryDelay

Question 2

A production support console displays a customer-supplied subject using this statement:

subjectElement.innerHTML = subject;

A security review finds that a subject can inject HTML into the console. Subjects must be inserted as text, with no characters removed or interpreted as markup. subjectElement is an existing div, and subject is a string.

Select the replacement that removes this injection point without discarding legitimate text.

Accepted Answer

subjectElement.textContent = subject;

Answer

subjectElement.innerHTML = JSON.stringify(subject);

Answer

subjectElement.innerHTML = subject.replace(/<[^>]*>/g, "");

Answer

if (!/[<>]/.test(subject)) subjectElement.innerHTML = subject;

Question 3

An editor creates a draft of a saved profile:

const saved = {
  name: "Mira",
  preferences: { theme: "light" }
};
const draft = { ...saved };
draft.name = "Noor";
draft.preferences.theme = "dark";

No save operation has run. At this point, what are saved.name and saved.preferences.theme, respectively?

Accepted Answer

"Mira" and "dark"

Answer

"Mira" and "light"

Answer

"Noor" and "dark"

Answer

"Noor" and "light"

Question 4

A browser application reads quantities from form controls, calculates invoice totals, and writes the results into a table. A Node.js batch job must reuse the same calculation rules without loading or emulating a web page.

Which design separates reusable JavaScript from browser-only functionality?

Accepted Answer

Put the calculation in a function that accepts values; keep DOM access in the browser.

Answer

Export the existing calculation function with its document queries intact, then import it into Node.js.

Answer

Move the form elements into the shared module so the batch job can read their current values.

Answer

Declare the existing DOM-based function async so it can execute without a browser document.

Question 5

An export must skip draft records, stop entirely at the first blocked record, and export every other record encountered before that point. Each record has exactly one status.

for (const record of records) {
  if (record.status === "draft") {
    // statement 1
  }
  if (record.status === "blocked") {
    // statement 2
  }
  exportRecord(record);
}

Which pair belongs at statements 1 and 2?

Accepted Answer

continue; then break;

Answer

break; then continue;

Answer

continue; then continue;

Answer

break; then break;

Question 6

A browser fetch call receives HTTP 503 with valid JSON. In this code, showReport displays the JSON error object instead of showFailure running:

fetch("/api/report")
  .then(response => response.json())
  .then(showReport)
  .catch(showFailure);

Neither display function throws. What change sends unsuccessful HTTP responses to showFailure while retaining JSON parsing for successful responses?

Accepted Answer

Check response.ok in the first then callback and throw when it is false before parsing.

Answer

Wrap the existing chain in a synchronous try/catch without awaiting it, leaving the callbacks unchanged.

Answer

Move catch immediately after fetch so it receives unsuccessful server responses before JSON parsing.

Answer

Append a second catch after showFailure so HTTP errors have a separate rejection handler.

Question 7

The documentation for an import API states:

readBatch(file) returns a Promise.
On fulfillment: { accepted: [...], rejected: [...] }
Each rejected entry contains a row number and an error message.
Invalid rows do not reject the Promise.
The Promise rejects only if the file cannot be read.

A readable file contains both valid and invalid rows. The import screen must process the valid rows and show the invalid rows' messages. Which handling follows the documented contract?

Accepted Answer

Await the result, process accepted, and display the messages in rejected.

Answer

Reject the entire batch whenever rejected is nonempty, withholding the valid rows until all errors are fixed.

Answer

Process accepted in then and handle invalid-row messages in catch, since both are reported as rejections.

Answer

Read accepted directly from the returned Promise and reserve finally for messages about invalid rows.

Question 8

A product selector must return the SKU strings of the two cheapest in-stock products, in ascending price order, without changing catalog or its objects. All prices are distinct finite numbers.

const catalog = [
  { sku: "A", price: 5,  inStock: false },
  { sku: "B", price: 30, inStock: true },
  { sku: "C", price: 20, inStock: true },
  { sku: "D", price: 10, inStock: true }
];

Only one expression satisfies both the selection rule and the no-mutation requirement. Identify it.

Accepted Answer

catalog.filter(p => p.inStock).sort((a, b) => a.price - b.price).slice(0, 2).map(p => p.sku)

Answer

catalog.sort((a, b) => a.price - b.price).filter(p => p.inStock).slice(0, 2).map(p => p.sku)

Answer

catalog.filter(p => p.inStock).slice(0, 2).sort((a, b) => a.price - b.price).map(p => p.sku)

Answer

[...catalog].sort((a, b) => a.price - b.price).slice(0, 2).filter(p => p.inStock).map(p => p.sku)

Question 9

A developer expects this returned function to report the phase that existed when the arrow function was created:

function makeReporter() {
  let phase = "queued";
  const report = () => phase;
  phase = "sent";
  return report;
}

const report = makeReporter();

The developer now calls report(). Which result and explanation are correct?

Accepted Answer

It returns "sent" because the closure reads the retained phase binding.

Answer

It returns "queued" because creating the arrow copies the current string value.

Answer

It returns undefined because the outer function has already finished executing.

Answer

It throws ReferenceError because phase is outside the scope of the caller.

Question 10

A log parser recognizes sale and return references:

const match = /(?:sale|return)-([A-Z]{2})-(\d{4})/
  .exec("return-GB-4827");

The interface needs the four-digit identifier as a string, without the transaction type or region. Select the expression that produces "4827".

Accepted Answer

match[2]

Answer

match[0]

Answer

match[1]

Answer

match[3]

Free TJ Practice Questions

Domain 1: Fundamentals and Applications

Question 1

Domain 2: Language and Syntax

Question 2

Question 3

Question 4

Domain 3: Data Structures and Objects

Question 5

Question 6

Domain 4: Packages and APIs

Question 7

Question 8

Question 9

Domain 5: Applied JavaScript

Question 10

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