What Happens When You Subtract a Number from a String in JavaScript? – Tech Mahindra Interview Question.

Our Javascript Code Expression

console.log("5" - 5);

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❓ What’s Happening Here?

We’re subtracting a number from a string.

"5" - 5

JavaScript sees that you’re using the - operator. which is strictly arithmetic, not string concatenation so it automatically tries to convert both operands to numbers.

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Step-by-Step Breakdown

🔸 Step 1: Identify the types

• "5" → string
• 5 → number

🔸 Step 2: Apply Type Coercion

• When using the - operator, JavaScript will convert "5" to a number before subtraction.
• "5" → 5 (string to number)

🔸 Step 3: Subtract

5 - 5 = 0

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✔ Final Answer:

B) 0

This question appeared in the Tech Mahindra 2nd round of interview, testing the candidate’s knowledge of type coercion of number and string when using minus (-) operator in JavaScript.

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🧠 Why Didn’t It Concatenate?

Great question! That’s because JavaScript behaves differently depending on the operator:

➕ The + Operator

• If one operand is a string, JavaScript concatenates.
• Example:

        console.log("5" + 5); // "55"

➖ The -, *, /, % Operators

• These are pure arithmetic.
• JavaScript will always try to convert both operands to numbers before the operation.

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🧪 Bonus Examples

console.log("10" - "3"); // 7
console.log("10" * "2"); // 20
console.log("10" / "2"); // 5
console.log("10" - true); // 9 (true → 1)
console.log("10" - false); // 10 (false → 0)

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Remember Key Takeaways

Operator	Behavior with Strings
+	Concatenates if either operand is a string
- * /	Converts to numbers and performs math

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JavaScript is flexible, but sometimes sneaky! If you're ever unsure, just ask: “Is this operator for math or for strings?” That usually clears it up. Want to try some tricky ones with null, undefined, or arrays next?