JavaScript-Developer-I Practice Questions

The correct answers are A and B .

The original question contains a typing error where 66 should be corrected to the logical AND operator:

& &

A is correct because it first evaluates the logical AND expression and then converts the final result to a Boolean:

Boolean(exp1 & & exp2)

The & & operator returns the first falsy value or the last truthy value. Wrapping the result in Boolean() ensures the final result is strictly either:

true

or:

false

Example:

Boolean( " hello " & & 123);

This returns:

true

B is also correct because it converts both expressions to Boolean values first, then applies logical AND:

Boolean(exp1) & & Boolean(exp2)

This guarantees that both sides of the & & operation are Boolean values.

Example:

Boolean( " hello " ) & & Boolean(123);

This returns:

true

C is incorrect because it uses the bitwise AND operator:

&

This is not the same as logical AND:

& &

Bitwise AND converts values into numbers and compares their binary representation. It does not reliably return a Boolean logical result.

D is incorrect as written because the question gives the expressions as exp1 and exp2, but option D uses var1 and var2. After correction, it would be the same idea as option

B.  

Therefore, the verified answers are A and B .

The correct answers are A, B, and C .

The original variable name appears to contain a typing error. The variable should be used consistently as sampleText:

let sampleText = " The quick brown fox jumps " ;

A is correct because includes() checks whether a string contains a specific substring and returns a Boolean value:

sampleText.includes( ' fox ' );

Since " fox " exists inside " The quick brown fox jumps " , this returns:

true

B is correct after correcting the typing error. The correct expression is:

sampleText.indexOf( ' quick ' ) > -1;

indexOf() returns the index position where the substring is found. If the substring is not found, it returns -1.

Since " quick " exists in the string, sampleText.indexOf( ' quick ' ) returns a value greater than -1, so the expression returns:

true

C is correct after correcting the missing quotation marks and adding a Boolean comparison:

sampleText.indexOf( ' fox ' ) !== -1;

The substring " fox " exists in the string, so indexOf( ' fox ' ) does not return -1. Therefore, the expression returns:

true

D is incorrect because the method name is typed incorrectly. JavaScript string has includes(), not include().

Incorrect:

sampleText.include( ' fox ' )

Correct:

sampleText.includes( ' fox ' )

E is incorrect because JavaScript string matching is case-sensitive:

sampleText.indexOf( ' Quick ' ) !== -1;

The string contains " quick " with a lowercase q, not " Quick " with an uppercase Q, so this returns:

false

Therefore, the verified answers are A, B, and C .

When execution hits the debugger; statement on line 06, JavaScript execution pauses at that point. Most modern browsers (for example, using DevTools) allow you to inspect the current scope , DOM, and various browser APIs in the console.

Let’s look at what is available precisely at line 06.

Current code state at the breakpoint:

Lines 01–04 define the Car constructor function.

Line 05 executes:

let carSpeed = document.getElementById( ' carSpeed ' );

So at line 06:

carSpeed is a variable containing a reference to a DOM element (the element with id " carSpeed " ).

Line 07 has not executed yet:

let fourWheels = new Car(carSpeed.value, ' red ' );

So fourWheels has not been created and is not accessible yet (it is in the temporal dead zone for the let declaration).

Now check each option:

Option A:

" A variable displaying the number of instances created for the Car object "

This code does not implement any mechanism to count instances of Car.

There is no static property, global counter, or similar variable tracking the number of Car instances.

At line 06, no instance of Car has even been created yet (new Car(...) is on line 07, which has not run).

Therefore, there is no such variable by default in JavaScript or DevTools.

This option is not available.

Option B:

" The information stored in the window.localStorage property "

At a breakpoint, the console is fully usable to inspect global objects.

window.localStorage is always accessible from the console (assuming standard browser context).

You can type:

window.localStorage

and inspect key/value pairs stored there.

This is independent of the current function or breakpoint line; localStorage is part of the Web Storage API on the window object.

So this information is indeed available in the console at line 06.

Option C:

" The values of the carSpeed and fourWheels variables "

At line 06:

carSpeed has been declared and assigned (line 05), so it is available, and its value (a DOM element) can be inspected.

fourWheels is declared on line 07 with let and has not yet been executed.

Variables declared with let and const are in a temporal dead zone before their declaration line completes.

At line 06, fourWheels is not yet initialized, and attempting to access it would result in a ReferenceError.

Thus, you can inspect carSpeed but not fourWheels. The option explicitly says " the values of the carSpeed and fourWheels variables " , which is not correct at this breakpoint, because fourWheels is not available yet.

Option D:

" The style, event listeners and other attributes applied to the carSpeed DOM element "

carSpeed holds a reference to a DOM element (document.getElementById( ' carSpeed ' )).

In DevTools, you can inspect this element in several ways:

Typing carSpeed in the console.

Inspecting it in the Elements panel.

From the console or Elements panel, you can view:

Its style (inline styles and computed styles).

Event listeners attached to it (using event listener viewer in DevTools).

Other attributes (id, class, etc.).

All of this is accessible at the point where execution is paused.

Therefore, this information is available at the breakpoint.

Conclusion:

B is available (global window.localStorage).

D is available (full inspection of the carSpeed DOM element).

A is not present in this code or environment.

C is partially wrong (only carSpeed exists; fourWheels does not yet).

So the two correct answers are:

Answer: B, D

References of JavaScript knowledge documents or Study Guide (concept names only):

debugger statement and pausing execution

JavaScript execution context and scope at a breakpoint

let declarations and temporal dead zone

Browser DevTools console and inspection of variables

DOM access via document.getElementById and inspection of elements

Web Storage API: window.localStorage