Salesforce Updated JavaScript-Developer-I Exam Questions and Answers by yara

The syntax:

import printPrice from ' module ' ;

means the module must export its function as a default export :

export default function printPrice() { ... }

Why the others are wrong:

Named exports require curly braces:

import { printPrice } from ' module ' ;

“all export” and “multi export” are not JavaScript terms.

Therefore, printPrice must be the default export .

JavaScript Knowledge References (text-only)

Default imports use: import name from ' module ' .

Named imports require braces: import { name } from ' module ' .

A subclass created by:

Console16bit.prototype = Object.create(GameConsole.prototype);

inherits all prototype methods from GameConsole, including load.

To override the inherited method, the correct syntax is to assign a new function to the method name on the prototype:

Console16bit.prototype.load = function(gamename) {

console.log(`${this.name} is loading a cartridge game: ${gamename}....`);

};

Why the other options are wrong:

A assigns something to the constructor function itself, not to the prototype method. Invalid.

B attempts to call a function in the left-hand side of an assignment; invalid syntax.

C also uses invalid syntax—prototype methods cannot be defined this way.

D is the correct definition of a prototype method override.

JavaScript Knowledge References (text-only)

Methods are overridden by assigning functions to Subclass.prototype.methodName.

Object.create() establishes prototype inheritance.

Constructor functions require prototype method attachment using assignment syntax.

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This question tests understanding of let (block scope) and var (function scope) in JavaScript.

Initial declarations in the function:

let x = 1; // line 2

var y = 1; // line 3

Here:

x is declared with let, so it is block-scoped to the function body.

y is declared with var, so it is function-scoped to the entire function.

Inside the if (reassign) block (and since reassign is true, we enter it):

if (reassign) {

let x = 2; // line 6

var y = 2; // line 7

console.log(x); // line 8

console.log(y); // line 9

}

Detailed behavior:

let x = 2; on line 6 creates a new block-scoped variable x that exists only inside the if block. It does not change the outer x declared on line 2.

var y = 2; on line 7 declares y with var again, but var is function-scoped. This effectively reassigns the same y defined on line 3 for the entire function. After this line, y is 2 everywhere in the function.

Now, inside the if block:

console.log(x); (line 8) logs the inner block-scoped x, which is 2.

console.log(y); (line 9) logs y, which is the function-scoped y that was set to 2.

So the first two outputs are:

2

2

After the if block, execution continues:

console.log(x); // line 12

console.log(y); // line 13

Outside the if block:

The block-scoped let x = 2; no longer exists; it was only visible inside the if block.

The outer let x = 1; (line 2) is still in scope and has not been changed.

Thus:

console.log(x); (line 12) logs the outer x, which is still 1.

console.log(y); (line 13) logs y which, due to var y = 2; inside the if, is now 2 for the whole function.

Therefore, when myFunction(true) is called, the output in order is:

2 (inner x in if)

2 (function-scoped y after reassignment)

1 (outer x after if)

2 (function-scoped y remains 2)

This corresponds to:

Answer: B (2 2 1 2)

JavaScript knowledge / study guide reference concepts:

let declarations and block scope

var declarations and function scope

Shadowing of variables with let inside a block

Re-declaration and reassignment of var within a function

Execution order of statements and console output

Key JavaScript Promise rule:

try...catch does not catch asynchronous errors that occur in Promise chains.

Therefore, the correct way to handle errors in a Promise is:

promise.then(...).catch(...);

Analysis of options:

A and B: Both wrap asynchronous code in try...catch, which does not catch Promise rejections. try...catch only catches errors thrown synchronously inside the block.

C: Correct. A .catch() on the Promise chain handles any error from the Promise returned by requestPromise().

D: .finally() executes regardless of success or failure, but it does not receive the error object , so it cannot handle the error.

Thus the only valid solution is option C .

JavaScript Knowledge References (text-only)

Promise rejections must be handled with .catch().

try...catch only handles synchronous code.

.finally() does not receive a rejection reason.

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