JavaScript Logical Operators (|| and &&) Explained with Examples – Asked in an HCL Tech Interview

Our Code Expressions:

console.log(0 || 1);  // ?
console.log(1 || 2);  // ?
console.log(0 && 1);  // ?
console.log(1 && 2);  // ?

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First, Understand the Logical Operators:

1. || (Logical OR)

• Returns the first truthy value it finds.
• If none are truthy, it returns the last value.
• It short-circuits, stops evaluating once it finds a truthy value.

2. && (Logical AND)

• Returns the first falsy value it finds.
• If none are falsy, it returns the last value.
• It also short-circuits, stops evaluating once it finds a falsy value.

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Expression-by-Expression Breakdown

console.log(0 || 1);

• 0 is falsy
• 1 is truthy
• || finds that 0 is falsy, so it keeps going and returns 1.

Output:

1

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console.log(1 || 2);

• 1 is truthy, so || returns it immediately without checking 2.

Output:

1

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console.log(0 && 1);

• 0 is falsy, so && stops and returns it right away.
• Doesn’t even look at 1.

Output:

0

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console.log(1 && 2);

• 1 is truthy, so && evaluates the second operand.
• 2 is also truthy, so it returns the last value.

Output:

2

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✔ Final Answer:

A) 1 1 0 2

This question appeared in the HCL Tech interview, testing the candidate’s knowledge of boolean AND (&&) and OR (||) operator in JavaScript.