Salesforce Developer JavaScript-Developer-I Full Course Free

We already know NaN is special: it is not equal to itself.

Check each:

A. value === Number.NaN

Number.NaN is NaN.

NaN === NaN is always false.

This will never be true; cannot reliably detect NaN.

B. value == NaN

NaN == NaN is also always false.

Again, this never detects NaN.

C. isNaN(value)

Global isNaN converts its argument to a number and then checks if the result is NaN.

This can detect NaN, but it may also return true for non-number values that coerce to NaN, such as isNaN( ' foo ' ).

Regardless, it is a standard way to detect if a value is “NaN-like” in JavaScript.

D. Object.is(value, NaN)

Object.is(NaN, NaN) returns true.

This is a strict way to detect a value that is exactly NaN (no coercion).

Therefore, among the given choices, the two viable ways to detect NaN are:

isNaN(value)

Object.is(value, NaN)

In JavaScript, NaN has some special properties:

NaN is not equal to anything, including itself.

Equality operators (==, ===) do not work for detecting NaN.

Check each option:

A. value === Number.NaN

Number.NaN is just NaN.

But NaN === NaN is always false.

So this expression is never true and cannot be used to detect NaN.

B. value == NaN

Same issue. NaN == NaN is always false.

So this also never detects NaN.

C. Object.is(value, NaN)

Object.is is a more precise equality comparison method.

It treats NaN as equal to NaN: Object.is(NaN, NaN) is true.

So Object.is(value, NaN) is a valid way to detect NaN.

D. value !== value

Because NaN is the only JavaScript value that is not equal to itself , value !== value is true only when value is NaN.

This is a classic trick for NaN detection.

E. Number.isNaN(value)

Number.isNaN is the recommended modern way to check if a value is NaN without coercion .

It returns true only if value is actually the number NaN.

Therefore, the three correct ways are:

Object.is(value, NaN)

value !== value

Number.isNaN(value)

In Node.js:

__filename is the absolute path to the current file (including file name).

__dirname is the absolute path to the directory that contains the current file.

window.location is a browser-only global, not available in Node.js.

this.path is not a standard Node.js global for path information.

The requirement is:

“the folder location that the code executes from.”

That is exactly what __dirname provides.

So the correct choice is __dirname.

Concepts: Node.js globals, __filename, __dirname, Node vs browser environment.

The correct answers are A and C because both use named exports for foo and bar.

A module can export multiple values by name:

export { foo, bar };

This allows another file to import them like this:

import { foo, bar } from ' ./utils.js ' ;

Option A is correct because it defines both functions locally and exports both of them as named exports.

const foo = () = > { return ' foo ' ; };

const bar = () = > { return ' bar ' ; };

export { foo, bar };

Option C is also correct after correcting the typing issue so that both foo and bar are imported first:

import { foo, bar } from " ./helpers/utils.js " ;

export { foo, bar };

This is called re-exporting. The module imports foo and bar from another module, then exports them again from utils.js.

Option B is not the best answer for named access because it exports one default object:

export default { foo, bar };

That would require a default import first:

import utils from ' ./utils.js ' ;

utils.foo();

utils.bar();

It does not directly support named imports in the same way as:

import { foo, bar } from ' ./utils.js ' ;

Option D exports a default class. Its foo() and bar() are class instance methods, not named exported functions. It would require usage like:

import Utils from ' ./utils.js ' ;

const utils = new Utils();

utils.foo();

utils.bar();

So for direct multiple function exports, the correct implementations are A and C .