1

What is the output of the following code?
const arr = [1, 2, 3]; const [a, , b] = arr; console.log(a, b);

A1 2 B1 3 C2 3 Dundefined 3

2

Which keyword should be used to declare a variable that is block-scoped and cannot be reassigned?

Avar Blet Cconst Dstatic

3

What does the spread operator (...) do when used with an array?

AExpands the array's elements into individual values BCreates a deep copy of the array CMerges two arrays into a nested array DReverses the array elements

4

Which of the following correctly defines an arrow function that takes two parameters and returns their sum?

Afunction (a, b) => a + b B=> (a, b) { return a + b; } Cconst add = (a, b) { return a + b; } Dconst add = (a, b) => a + b;

5

What is a closure in JavaScript?

AA way to close the browser window using JavaScript BA function that retains access to its outer scope's variables even after the outer function has returned CA method to terminate an event listener DA class that encapsulates private fields

6

What is the correct syntax for a template literal that includes a variable?

A"Hello " + {name} B'Hello #{name}' C`Hello ${name}` D"Hello $[name]"

7

What does Promise.all() return if one of the promises in the array rejects?

AA rejected promise with the reason of the first rejected promise BA resolved promise with the results of all fulfilled promises CAn array with null for the failed promise DIt waits for all promises to settle before resolving

8

Which LWC decorator is used to expose a property or method so a parent component can access it?

A@track B@wire C@import D@api

9

In LWC, which lifecycle hook is called after the component's element is inserted into the DOM?

Aconstructor() BconnectedCallback() CrenderedCallback() DdisconnectedCallback()

10

What is the correct way to export a function named greet as a named export from a JavaScript module?

Amodule.export = function greet() {} Bexport default function greet() {} Cexport function greet() {} Dpublic function greet() {}

11

Which method is used to make an HTTP request using the modern browser API (without third-party libraries)?

Afetch() BXMLHttpRequest.get() Chttp.get() Drequest()

12

In an LWC component, the @wire decorator is used to:

AExpose a property to a parent component BImperatively call an Apex method CDefine a reactive private property DRead data from Salesforce using an Apex method or wire adapter reactively

13

What is the purpose of async/await in JavaScript?

ATo run multiple functions simultaneously in parallel threads BTo write asynchronous code in a synchronous-looking style using Promises CTo make functions return immediately without waiting DTo create Web Workers for background processing

14

Which of the following correctly demonstrates object destructuring in ES6?

Aconst name = person['name']; Bconst (name, age) = person; Cconst { name, age } = person; Dconst [name, age] = person;

15

In JavaScript, what does the typeof operator return for null?

A"object" B"null" C"undefined" D"boolean"

16

Which method is used in Jest to create a mock function that can track calls and return values?

Ajest.spy() Bjest.stub() Cjest.mock() Djest.fn()

17

In the Module design pattern, what is the main purpose?

ATo allow multiple instances of a class BTo encapsulate private state and expose a public API CTo observe changes to a DOM element DTo ensure asynchronous code runs synchronously

18

What is the difference between == and === in JavaScript?

AThere is no difference; both perform the same comparison B== compares by reference; === compares by value C== performs type coercion; === checks both value and type without coercion D=== is only valid in strict mode

19

Which LWC lifecycle hook is invoked each time the component finishes rendering?

ArenderedCallback() BconnectedCallback() Cconstructor() DerrorCallback()

20

What does the rest parameter (...args) do in a function definition?

ASpreads an array into individual arguments BCreates a copy of the arguments object CReturns the remaining string after a split DCollects all remaining arguments into an array

21

In JavaScript classes (ES6+), what is the purpose of the super() call inside a constructor?

ATo call a static method of the parent class BTo invoke the parent class's constructor and initialize inherited properties CTo override the parent class's constructor entirely DTo access the parent class's private fields

22

How does an LWC child component communicate an event upward to its parent?

ABy calling a method directly on the parent component reference BBy modifying a shared global variable CBy dispatching a CustomEvent using this.dispatchEvent() DBy importing the parent component's module

23

Which Jest matcher verifies that a function was called a specific number of times?

AtoHaveBeenCalledTimes(n) BtoBeCalledWith(n) CtoHaveCallCount(n) DtoBeInvokedTimes(n)

24

What is "hoisting" in JavaScript?

AThe process of moving code to a CDN BMaking a variable available inside a loop CCompiling JavaScript before execution DJavaScript's behavior of moving variable and function declarations to the top of their scope before execution

25

In the Observer design pattern, what role does the subject play?

AIt listens for changes from other objects BIt maintains a list of observers and notifies them when its state changes CIt is the singleton instance of a class DIt creates a proxy object for another object

26

What is the output of console.log(0.1 + 0.2 === 0.3); in JavaScript?

Atrue B1 Cfalse DNaN

27

In Aura framework, which method is used to create a component dynamically at runtime?

A$A.createComponent() B$A.instantiateComponent() C$A.newComponent() D$A.buildComponent()

28

Which of the following correctly imports a default export from a module named "utils.js"?

Aimport { utils } from './utils.js'; Brequire('./utils.js'); Cimport * from './utils.js'; Dimport utils from './utils.js';

29

Which DOM method selects the first element matching a CSS selector?

Adocument.getElementById() Bdocument.querySelector() Cdocument.getElementsByClassName() Ddocument.selectElement()

30

In the Singleton pattern, what guarantees that only one instance of a class is created?

AUsing the final keyword on the class BDeclaring the constructor as async CChecking if an instance already exists and returning it if so, using a private static reference DUsing a WeakMap to store the instance

31

In Node.js, which global object provides information about the current module's file path?

A__dirname and __filename Bprocess.path Cmodule.path Dglobal.filePath

32

What does event.preventDefault() do in JavaScript event handling?

AStops the event from being created BRemoves all event listeners from the element CStops the event from bubbling up the DOM DCancels the browser's default action associated with the event

33

Which array method returns a new array containing only the elements that pass a test function?

AArray.reduce() BArray.filter() CArray.find() DArray.some()

34

In LWC, the Shadow DOM ensures that:

AAll components share the same CSS styles globally BJavaScript in a child component can directly access the parent's DOM CA component's internal DOM is encapsulated and isolated from outside styles and scripts DComponent templates are compiled server-side

35

What is the correct way to handle errors in an async/await function?

AWrap the await call in a try/catch block BUse .catch() directly on the await expression CUse window.onerror to catch all errors DAsync functions cannot throw errors

36

In JavaScript, which statement about let and var is TRUE?

ABoth var and let are function-scoped Blet variables are hoisted without a Temporal Dead Zone Cvar is block-scoped like let Dvar is function-scoped and hoisted; let is block-scoped and has a Temporal Dead Zone

37

Which Node.js module is used to work with file paths in a cross-platform manner?

Afs Bpath Curl Dos

38

What is the primary difference between Promise.all() and Promise.allSettled()?

APromise.all() is faster than Promise.allSettled() BPromise.allSettled() rejects immediately if one promise fails CPromise.allSettled() waits for all promises to settle (resolve or reject) and returns all results; Promise.all() short-circuits on the first rejection DPromise.all() returns results regardless of rejection; Promise.allSettled() requires all to resolve

39

In an LWC component, which method is used to access a child element in the template using a template reference?

Athis.template.querySelector() Bdocument.querySelector() Cthis.refs.elementName Dthis.shadowRoot.getElementById()

40

What does the Array.prototype.map() method return?

AA boolean indicating if the mapping succeeded BThe original array with modified elements in place Cundefined DA new array with the results of calling the callback on every element

41

In JavaScript, what is the prototype chain used for?

ATo define the order of CSS style application BTo look up properties and methods on an object through a chain of prototype references CTo chain multiple Promises together DTo determine the scope of a variable

42

What is the purpose of jest.mock('moduleName') in a Jest test?

ATo execute the module in isolation BTo spy on specific functions within the module CTo replace the module with an auto-mocked version for the test DTo import the module asynchronously

43

What happens when you use var inside a for loop in JavaScript?

AThe variable is hoisted to function scope and accessible outside the loop BThe variable is block-scoped and cannot be accessed outside the loop CThe variable is deleted after each iteration DA new variable is created for each iteration

44

In the Aura framework, which attribute is used to pass data from a parent component to a child component?

A<aura:handler> B<aura:event> C<aura:method> D<aura:attribute> with access="global"

45

Which ES6 feature allows you to define default values for function parameters?

AParameter spread BDefault parameter values: function greet(name = 'World') {} COptional chaining DNullish coalescing assignment

46

In JavaScript, which statement about arrow functions and this is TRUE?

AArrow functions create their own this binding BArrow functions cannot access this at all CArrow functions inherit this from their enclosing lexical scope DArrow functions always bind this to the global object

47

What is the correct way to create an LWC component that listens for a platform event using the wire service?

AUse the @wire(MessageContext) decorator and subscribe via the Lightning Message Service BUse window.addEventListener() directly in connectedCallback CImport the platform event and call subscribe() from the Streaming API module DUse @api onplatformevent decorator

48

Which method stops event propagation in the DOM so parent elements do not receive the event?

Aevent.preventDefault() Bevent.cancelBubble() Cevent.removeEventListener() Devent.stopPropagation()

49

In Jest, which function is used to group related test cases together?

Atest() Bdescribe() Cit() Dgroup()

50

What is the output of:
const obj = {a: 1}; const copy = {...obj, b: 2}; console.log(copy);

A{a: 1} B{b: 2} C{a: 1, b: 2} D{obj: {a:1}, b: 2}

Salesforce Certified JavaScript Developer I Mock Test