The question states that the DataPrettyPrint module has one default export, the function printDate(). According to the ECMAScript (ES6) module specification, which Lightning Web Components use, a default export is imported without curly braces {}. The developer can assign any valid name to the imported function. Option B correctly imports the default function, assigns it the local name myPrintDate, and then invokes it. This syntax is the standard and correct way to handle default imports.

A: This syntax, using curly braces {}, is for importing named exports. The question specifies a default export, making this syntax incorrect.

C: While the import statement itself is syntactically correct for a default export, the function call DataPrettyPrint.printDate() is wrong. The default export is assigned directly to the printDate identifier, not as a property of an object named after the module.

D: This syntax import { ... as ... } is used for importing and renaming a named export. It is not the correct syntax for a default export.

1. Salesforce Lightning Web Components Dev Guide: In the "Share JavaScript Code" section, under "JavaScript Modules," the documentation explicitly differentiates between named and default exports. It states, "To import the default export, don’t use curly braces." It provides an example: import util from 'c/utils';, which directly matches the syntax used in the correct answer.

Reference: Lightning Web Components Dev Guide > Developer Tools > Share JavaScript Code > JavaScript Modules.

2. MDN Web Docs (Mozilla): The official Mozilla documentation for JavaScript provides a definitive guide on import and export syntax.

For import, it specifies the syntax for importing defaults as: import defaultExport from "module-name";. This confirms that a custom name can be assigned to the default export without using curly braces.

Reference: MDN Web Docs, import statement, "Importing defaults" section.

3. Exploring ES6 (by Dr. Axel Rauschmayer): This peer-reviewed book on JavaScript features is a highly respected academic resource.

In Chapter 17, "Modules," Section 17.3.2, "Default exports (one per module)," it explains that a default export is imported with the syntax import myIdentifier from 'src/mylib';. This directly supports the structure of the correct answer.

Reference: Rauschmayer, A. (2015). Exploring ES6. Chapter 17, Section 17.3.2.

The setTimeout function schedules a function to be executed after a specified delay. The first argument must be a function reference.

Option C correctly uses an anonymous arrow function () => { formatName("John', 'Doe') } as the callback. This creates a new function that, when executed by setTimeout after 5000ms, will then call formatName with the desired arguments. This is a standard and secure method for deferring a function execution with parameters. Note that the option contains typos (setTimout and mismatched quotes), but the programming pattern it represents is the correct one among the choices.

A. setTimeout (formatName(), 5000, "John", "BDoe");

This option invokes formatName() immediately and passes its return value (a string) to setTimeout, not the function itself.

B. setTimeout (formatName('John', ‘'Doe'), 5000);

Similar to option A, this invokes formatName() immediately. The function should be executed after the delay, not before.

D. setTimeout ('formatName', 5000, 'John", "Doe');

Using a string as the first argument is a legacy, insecure practice equivalent to eval(). Furthermore, passing additional parameters to the callback is not supported with this string syntax.

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1. MDN Web Docs, WindowOrWorkerGlobalScope.setTimeout():

Section: Syntax: The documentation specifies the recommended syntax as setTimeout(functionRef, delay, param1, param2, ...) where functionRef is a reference to a function.

Section: The 'this' problem: This section provides an example of using a wrapper function (anonymous function) to solve context and parameter issues, validating the pattern in option C: setTimeout(() => { myObj.myMethod('param1', 'param2'); }, 0);

Section: Notes (on string literals): The documentation explicitly warns against using strings: "For historical reasons, you can pass a string instead of a function... This is not recommended for the same reasons that using eval() is a security risk." It also states, "Passing additional parameters to the function in the first parameter is not supported in this syntax," which directly invalidates option D.

2. Salesforce Lightning Web Components Developer Guide:

Section: Use Third-Party JavaScript Libraries > setTimeout() and setInterval(): The guide demonstrates the use of standard JavaScript setTimeout, including clearing it in the disconnectedCallback, confirming that standard, modern JavaScript practices (like the one in option C) are expected. It does not mention or endorse the legacy string syntax.

Explanation:

Z is equal to 3.14

Use strict has effect only on line 5.

Line 5 throws an error

The Array.prototype.reduce() method executes a user-supplied "reducer" callback function on each element of the array, in order, passing in the return value from the calculation on the preceding element. The final result of running the reducer across all elements of the array is a single value.

When reduce() is called on an empty array and an initialValue is provided (in this case, 10), the callback function is never executed. Instead, the method immediately returns the provided initialValue. Therefore, calling myFunction with an empty array results in the return value of 10.

A. Returns 0: The provided initial value is 10. The function would only return 0 if that were the specified initial value.

B. Throws an error: A TypeError is thrown only when reduce() is called on an empty array without providing an initial value.

D. Returns NaN: NaN is not a possible outcome in this scenario, as the function is designed to return the defined initial value.

1. MDN Web Docs (Mozilla): Array.prototype.reduce()

Section: "Return value"

Content: "If the array is empty and initialValue is provided, initialValue will be returned without calling callbackFn." This directly confirms that for an empty array, the provided initial value is the return value.

2. ECMAScript® 2023 Language Specification (ECMA-262, 14th edition):

Section: 23.1.3.25 Array.prototype.reduce ( callbackfn [ , initialValue ] )

Content: The specification details the algorithm for reduce. In step 8, if the array length len is 0 and initialValue is not present, a TypeError is thrown. However, if initialValue is present (as it is in the question), step 9 states to return initialValue. This is the formal definition of the behavior.

3. University of Washington, CSE 154: Web Programming: Higher-Order Functions in JavaScript

Section: "Array reduce function"

Content: Course materials often explain that providing an initial value is a best practice to handle empty arrays gracefully, preventing errors and ensuring a predictable default return value, which is exactly the behavior tested in this question.

The JSON.stringify() method converts a JavaScript object to a JSON string. According to the JSON standard, functions are not a supported data type. Therefore, when the user object is stringified, the fullName property, which holds a function, is omitted from the resulting JSON string.

The JSON.parse() method then creates a new object, copiedUser, from this string. This new object will only contain the firstName and lastName properties. The subsequent line attempts to call copiedUser.fullName(), but since this property does not exist on copiedUser, its value is undefined. Attempting to invoke undefined as a function throws a TypeError.

A. Hello John Doe

This is incorrect because the fullName function is lost during the JSON.stringify process and does not exist on the copiedUser object, preventing a successful call.

B. Hello Dan

This is incorrect as the name "Dan" is not present in the code, and more importantly, the code fails with an error before it can produce any output.

C. Hello Dan Doe

This is incorrect for the same reasons as option B; the name is not in the code, and the execution halts due to a TypeError.

D. SyntaxError: Unexpected token in JSON

This is incorrect because the error is a TypeError, not a SyntaxError. A SyntaxError would occur if JSON.parse() received a malformed JSON string, but JSON.stringify() produces valid JSON.

1. MDN Web Docs (Mozilla): The JSON.stringify() documentation explicitly states its behavior with unsupported types.

Source: MDN Web Docs, JSON.stringify() method.

Reference: Under the "Description" section, it notes: "undefined, Function, and Symbol values are not valid JSON values. ...if any such values are encountered during conversion they are either omitted (when found in an object)..." This confirms the fullName property will be removed.

2. ECMAScript® 2023 Language Specification (ECMA-262, 14th edition): The official standard for JavaScript defines this behavior.

Source: ECMA-262, 14th Edition, June 2023.

Reference: Section 25.5.2, JSON.stringify ( value [ , replacer [ , space ] ] ). The internal abstract operation SerializeJSONProperty dictates that if the value of a property is a function, undefined, or a symbol, it returns undefined, which causes the property to be excluded from the final JSON object string.

The Promise.prototype.finally() method is invoked when a promise is settled. A promise is considered settled when it is no longer pending, meaning it has either been fulfilled (resolved) or rejected. The callback function provided to .finally() will execute regardless of the promise's outcome, making it suitable for cleanup operations that must occur after an asynchronous action completes, successful or not. In the provided code, the finally() block will run after either the .then() block (on resolution) or the .catch() block (on rejection) has executed.

A. When rejected: This is incomplete. The .finally() method also executes when the promise is successfully resolved.

B. When resolved and settled: This phrasing is redundant. A resolved promise is, by definition, a settled promise. This option incorrectly excludes the rejection case.

C. When resolved: This is incomplete. The .finally() method also executes when the promise is rejected.

1. MDN Web Docs (Mozilla): "The finally() method of a Promise schedules a function to be called when the promise is settled (either fulfilled or rejected). It immediately returns an equivalent Promise object, allowing you to chain calls to other promise methods."

Source: Promise.prototype.finally(), MDN Web Docs.

2. Salesforce Lightning Web Components Developer Guide: "To execute code whether the promise is fulfilled or rejected, use finally()."

Source: "Work with Promises" section, Lightning Web Components Developer Guide.

3. ECMAScript® 2022 Language Specification (ECMA-262, 13th edition): The specification defines the behavior of Promise.prototype.finally. The internal operations ensure that the onFinally function is called for both the fulfillment and rejection paths of the promise.

Source: Section 27.2.5.3, Promise.prototype.finally ( onFinally ).

Explanation:

Str.substring(0,5);

Str.substr(0,5);

The issue lies in how the input field's value is retrieved. The getAttribute('value') method reads the initial value of the value attribute as defined in the HTML source code, which is "Hello". This attribute value does not update when the user types into the field.

To access the current, live text content of the input field, you must use the element's value property (input.value). This property reflects the real-time data entered by the user and is the correct way to get the dynamic value from form elements.

B. getElementByName is not a valid DOM method. The correct method is getElementsByName, which returns a NodeList (a collection), not a single element, and does not solve the core issue.

C. The correct event type string for addEventListener is 'click'. The string 'onclick' is incorrect and would prevent the event listener from being attached properly.

D. addCallback is not a standard DOM method for attaching event listeners. The correct method is addEventListener.

1. MDN Web Docs (Mozilla): The HTMLInputElement.value property documentation explicitly states it contains the current value of the control. In contrast, the Element.getAttribute() documentation explains it returns the value of the attribute as specified in the HTML, which may not reflect the current state.

Source: MDN Web Docs, HTMLInputElement.value property. Section: "Value".

Source: MDN Web Docs, Element.getAttribute() method. Section: "Return value".

2. Salesforce Lightning Web Components Developer Guide: Examples of handling DOM events consistently use the addEventListener method with the standard 'click' event type, demonstrating the correct syntax used in modern web development within the Salesforce ecosystem.

Source: Lightning Web Components Developer Guide, Section: "Work with DOM APIs", Subsection: "Add and Remove Event Listeners".

3. WHATWG - HTML Living Standard: The official standard distinguishes between content attributes (from the HTML source) and IDL (Interface Definition Language) attributes, which are the live properties on the DOM object. For input elements, the value IDL attribute (property) reflects the current value, while the value content attribute reflects the default value.

Source: HTML Living Standard, Section 4.10.5.1.13 "The value attribute".

To add a CSS class to an HTML element using standard JavaScript, you first need to select the element. The document.querySelector('#row-uc') method correctly selects the single table row element with the ID row-uc. Once the element is selected, its classList property, which is a DOMTokenList, is used to manipulate its classes. The add() method of the classList object is the standard and correct way to append the specified class, 'priority-account', to the element's list of classes.

A. classes-push is not a valid property or method in the standard Document Object Model (DOM) API for class manipulation.

B. addClass() is a common method in JavaScript libraries like jQuery, but it is not a native method on DOM elements in vanilla JavaScript.

C. querySelectorAll() returns a NodeList (a collection of elements), not a single element. A NodeList does not have a classList property.

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1. Mozilla Developer Network (MDN) Web Docs on Element.classList: This document, considered an authoritative source for web standards, explains that classList is the standard property for accessing an element's classes and lists add() as the method for adding a class.

Source: MDN Web Docs, Element: classList property, Section: "Adding and removing classes". Available at: https://developer.mozilla.org/en-US/docs/Web/API/Element/classList

2. Mozilla Developer Network (MDN) Web Docs on Document.querySelector(): This documentation specifies that querySelector() returns the first Element that matches a specified CSS selector, which is the correct behavior needed to target a single element by its unique ID.

Source: MDN Web Docs, Document: querySelector() method. Available at: https://developer.mozilla.org/en-US/docs/Web/API/Document/querySelector

3. WHATWG - DOM Living Standard: The official standard for the Document Object Model defines the classList attribute on the Element interface.

Source: WHATWG, DOM Living Standard, Section 5.7.2 "The classList attribute". Available at: https://dom.spec.whatwg.org/#dom-element-classlist

The statement const arr = Array(5).fill(0) creates an array with two specific characteristics: its length is exactly 5, and every element within it is the number 0. The most accurate tests are those that precisely verify these two defining properties.

Option A, console.assert( arr.length === 5 ), correctly validates that the array has the exact length of 5.

Option B, arr.forEach(elem => console.assert(elem === 0)), iterates through every single element and asserts that its value is 0, comprehensively verifying the array's contents as intended by the .fill(0) method. Together, these two tests provide a complete and accurate validation of the array's state.

C. This assertion is logically flawed. arr[arr.length] (i.e., arr[5]) accesses an index outside the array's bounds (0-4), which returns undefined, causing the assertion undefined === 0 to fail.

D. This test is too general. While arr.length > 0 is true, it does not confirm the specific length of 5, making it less accurate than checking for the exact length.

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1. Mozilla Developer Network (MDN) Web Docs, Array.prototype.fill(): "The fill() method changes all elements in an array to a static value, from a start index (default 0) to an end index (default array.length). It returns the modified array." This supports option B's logic of checking every element's value.

Source: Mozilla, Array.prototype.fill(), Accessed [Current Date]. Available at: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/GlobalObjects/Array/fill

2. Mozilla Developer Network (MDN) Web Docs, Array.prototype.length: "The length data property of an Array instance represents the number of elements in that array... The value of the length property is an integer with a positive sign and a value less than 2^32." This supports option A's direct and precise check of the array's size.

Source: Mozilla, Array.prototype.length, Accessed [Current Date]. Available at: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/GlobalObjects/Array/length

3. ECMAScript® 2023 Language Specification (ECMA-262, 14th edition):

Section 10.4.2.1 [[Get]] ( P, Receiver ): This section defines array indexing. For an array of length L, valid integer indices P are from 0 to L-1. Any attempt to get an index equal to or greater than L does not retrieve an element from the array's internal storage, leading to undefined. This confirms why option C is incorrect, as arr[5] is out of bounds for an array of length 5.

Section 23.1.3.6 Array.prototype.fill ( value [ , start [ , end ] ] ): The specification details how this method fills every element from the resolved start to end index with the provided value. This underpins the correctness of option B's comprehensive check.