Postfix vs Prefix in JavaScript: Why console.log(x++ + ++y) Returns unexpected – JavaScript Increment Operators Explained. Asked in Infosys.

Our Javascript Code :-

let x = 1;
let y = 2;
console.log(x++ + ++y);

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1. Initial state

x === 1
y === 2

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2. The expression: x++ + ++y

JavaScript evaluates binary operators left‑to‑right, so:

1. Evaluate the left operand: x++
2. Evaluate the right operand: ++y
3. Add the two results
4. Print the sum

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2.1. Left operand: x++ (postfix increment)

• Postfix means:

1. Read the current value of x (which is 1).
2. Then increment x by 1.

• So the left side contributes 1 to the addition, and after reading it, x becomes 2.

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2.2. Right operand: ++y (prefix increment)

• Prefix means:

1. First increment y by 1.
2. Then read the new value of y.

• So the right side contributes 3 to the addition, and y is now 3.

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3. The addition and final result

Putting it together:

• Left operand gave 1
• Right operand gave 3
• Sum: 1 + 3 = 4

console.log(4); // prints 4
✔ Final Answer:
C) 4
This question appeared in the Infosys 1st round of interview, testing the candidate’s knowledge of Pre and Post Increment Operator in JavaScript.