Given two expressions var1 and var2. What are two valid ways to return the logical AND of the two expressions and ensure it is data type Boolean ?…

The logical AND (&&) operator in JavaScript evaluates operands and returns the value of the first falsy operand it encounters, or the value of the last operand if all are truthy. This returned value is not necessarily a boolean. To guarantee a boolean result, an explicit conversion is required.

Option A, Boolean(var1 && var2), first evaluates var1 && var2 and then explicitly converts the resulting value to a boolean using the Boolean() function.

Option D, Boolean(var1) && Boolean(var2), first converts each variable to a boolean and then performs the logical AND operation on the two resulting boolean values. Both methods correctly perform the logical AND and ensure the final data type is Boolean.

Why Incorrect Options are Wrong

B. var1 && var2

This expression returns the actual value of one of the operands, not necessarily a boolean. For example, 'a' && 'b' returns 'b'.

C. var1.toBoolean() && var2toBoolean()

The .toBoolean() method does not exist on standard JavaScript data types (like String, Number, etc.), and calling it would result in a TypeError.

References

1. MDN Web Docs (Mozilla): Logical AND (&&)

Reference: In the "Description" section, it states, "The logical AND (&&) operator... returns expr1 if it can be converted to false; otherwise, it returns expr2. Thus, when used with Boolean values, && returns true if both operands are true; otherwise, it returns false." This highlights that the return value is not always a boolean when used with non-boolean operands.

URL: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/LogicalAND

2. MDN Web Docs (Mozilla): Boolean

Reference: The documentation for the Boolean() function (when used without new) states: "The value passed as the first parameter is converted to a boolean value, if necessary." This confirms its role in explicit type coercion, which is central to options A and D.

URL: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/GlobalObjects/Boolean

3. ECMAScript® 2023 Language Specification (ECMA-262, 14th edition):

Reference: Section 13.13, "Binary Logical Operators", defines the runtime semantics for the && operator. The algorithm shows that it returns the value of one of the expressions (lval or rval), not necessarily a boolean primitive.

Reference: Section 7.1.2, "ToBoolean ( argument )", specifies the abstract operation for converting any ECMAScript language value to a boolean value, which is the underlying mechanism used by the Boolean() function.

URL: https://tc39.es/ecma262/#sec-binary-logical-operators and https://tc39.es/ecma262/#sec-toboolean