How && and || Operators Work in JavaScript – Asked in Mindtree's 2nd Round JavaScript Interview. Javascript interview prepration.

Understanding Logical Operators (|| and &&) in JavaScript

The given code uses logical OR (||) and logical AND (&&) operators with different values. Let’s break them down carefully.

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🔹 First Expression:

console.log(false || null || "Hello");

Step 1: Understanding the || (Logical OR) Operator

• The logical OR (||) operator returns the first truthy value it encounters.
• If all values are falsy, it returns the last falsy value.

Step 2: Evaluating the Expression (false || null || "Hello")

We evaluate from left to right:

1. false is falsy → move to the next operand.
2. null is also falsy → move to the next operand.
3. "Hello" is truthy → STOP and return "Hello".

➡ Output of First Expression:

Hello

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🔹 Second Expression:

console.log(false && null && "Hello");

Step 1: Understanding the && (Logical AND) Operator

• The logical AND (&&) operator returns the first falsy value it encounters.
• If all values are truthy, it returns the last truthy value.

Step 2: Evaluating the Expression (false && null && "Hello")

We evaluate from left to right:

1. false is falsy → STOP and return false (no need to check the rest).
2. null and "Hello" are ignored because && stops at the first falsy value.

➡ Output of Second Expression:

false

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Remember key points:

The logical && (AND) returns the first falsy value (or the last truthy value if all are truthy). The logical || (OF) returns the first truthy value (or the last falsy value if all are falsy).

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✔ Final Answer:

A) Hello false

This question appeared in the Mindtree 2nd round of interview, testing the candidate’s knowledge of Logical Operators like (&& and ||) operator in JavaScript.