Requirement:
getNextValue() should run only if handleObjectValue(x) does not throw an error.
If an error occurs, handleError(error) should run, and getNextValue() should be skipped.
Option B:
try {
handleObjectValue(x);
getNextValue();
} catch (error) {
handleError(error);
}
Behavior:
If handleObjectValue(x) succeeds (no error):
Execution continues to getNextValue();.
If handleObjectValue(x) throws:
Control jumps directly to catch, getNextValue() is skipped.
handleError(error); is called.
This matches the requirement perfectly.
Why others are incorrect:
A: } then { is invalid JavaScript syntax.
C:
try {
handleObjectValue(x);
} catch (error) {
handleError(error);
}
getNextValue();
getNextValue() is called after the try...catch regardless of whether an error occurred. Not acceptable.
D: finally always runs:
try {
handleObjectValue(x);
} catch (error) {
handleError(error);
} finally {
getNextValue();
}
getNextValue() will execute in both success and error cases.
Therefore, the correct approach is B.
Concepts: try/catch control flow, finally semantics, placing code inside vs outside try/catch blocks.

We want to guarantee that the result is of type string regardless of what var1 and var2 are (numbers, booleans, etc.).
Option A:
String(var1).concat(var2)
String(var1) converts var1 explicitly to a string.
.concat(var2) calls String.prototype.concat, which:
Converts var2 to string if needed.
Returns a new string that is the concatenation of the two.
Result is always a string.
So A is valid.
Option B:
String.concat(var1 + var2)
String.concat (as a static method) does not exist. concat is an instance method on string objects, not on the String constructor.
var1 + var2 might be a number (if both numeric) and used incorrectly here.
So B is invalid.
Option C:
var1 + var2
+ can mean:
String concatenation (if at least one operand is a string).
Numeric addition (if both operands are numbers).
If var1 and var2 are both numbers, var1 + var2 will be a number, not a string.
This does not ensure the result is always a string.
So C is not guaranteed to satisfy the requirement.
Option D:
var1.toString() + var2.toString()
var1.toString() converts var1 to a string (for most primitive/object types).
var2.toString() does the same.
Now both operands of + are strings, so the result is string concatenation.
Result is guaranteed to be a string.
So D is valid.
Therefore, the two valid ways are A and D.
Study Guide / Concept Reference (no links):
String() conversion vs .toString()
String.prototype.concat
+ operator overload: numeric addition vs string concatenation
Type coercion rules for primitives

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)