Handling Null u0026 Undefined Values Quiz Quiz

Explore how null and undefined values behave, differ, and are managed in programming. This quiz targets key concepts, behaviors, and practical cases to deepen your understanding of null and undefined handling in code.

1. Understanding Null vs Undefined

   In programming languages like JavaScript, what is the primary distinction between null and undefined when assigning them to a variable?

   1. Null is an explicit assignment; undefined means no value was assigned.
   2. Null indicates a syntax error; undefined is a valid value.
   3. Null and undefined can be used interchangeably in all operations.
   4. Null is a number type; undefined is a string type.

   Explanation: Null is typically used to intentionally assign a variable with 'no value', while undefined usually represents variables that have been declared but not yet assigned a value. Null does not indicate an error, and undefined is not always valid in every scenario. Null and undefined are not the same data type and their behavior differs in operations, so they are not interchangeable.

2. Comparing Null and Undefined

   When you compare null and undefined using the === operator in most programming languages, such as JavaScript, what is the result?

   1. null
   2. undefined
   3. true
   4. false

   Explanation: Using the strict equality operator (===) compares both value and type, so null === undefined returns false because the types are different. The answer 'true' would be correct for the loose equality operator (==), not the strict one. Options 'undefined' and 'null' are value types, not results of a comparison.

3. Default Parameter Values

   Given a function parameter with a default value, which input will result in the default value being used: a call with undefined or with null?

   1. Neither will use the default value; both use the passed value.
   2. Passing null will use the default value.
   3. Passing undefined will use the default value.
   4. Both null and undefined will trigger the default value.

   Explanation: When passing undefined as an argument, most languages with default parameters will assign the default value. Passing null does not trigger this; the value remains null. The statement that both will trigger the default is incorrect, and the last option incorrectly claims that neither use the default value.

4. Typeof Operator Results

   What does the typeof operator return for an uninitialized variable declared with let in JavaScript?

   1. string
   2. null
   3. object
   4. undefined

   Explanation: In JavaScript, uninitialized variables declared with let exist in the temporal dead zone and are technically uninitialized, so they have the value undefined if accessed before assignment. The typeof null is 'object', but that's not the case for undefined variables. The answers 'object' and 'string' do not apply here.

5. Handling Nullish Values Safely

   What is the primary purpose of a 'nullish coalescing operator' (often written as ??) in programming languages that support it?

   1. To trigger an exception for null values
   2. To compare two values for strict equality
   3. To provide a fallback value only if the original is null or undefined
   4. To automatically convert null and undefined to zero

   Explanation: The nullish coalescing operator (??) lets you specify a fallback value that applies when the first value is strictly null or undefined. It does not perform any value conversion, so it never converts null or undefined to zero. Comparing values and exception handling are unrelated to the function of this operator.