[Solved] Consider this NestJS pipe code snippet:transform(value: any) { const num = parseInt(value); if (!num) { throw new Error('Invalid number');... }What is the bug in this pipe when input is '0'? | NestJS

NestJS - Pipes

Consider this NestJS pipe code snippet:

transform(value: any) {
  const num = parseInt(value);
  if (!num) {
    throw new Error('Invalid number');
  }
  return num;
}

What is the bug in this pipe when input is '0'?

AIt throws an error incorrectly because !num is true for 0

BIt returns a string instead of a number

CIt does not parse the input at all

DIt always returns NaN

Step-by-Step Solution

Solution:

Step 1: Analyze the condition !num with input '0'
parseInt('0') returns 0, but !0 is true in JavaScript, so the error is thrown incorrectly.
Step 2: Identify the bug cause
The check should explicitly test for NaN, not falsy values, to avoid rejecting valid 0.
Final Answer:
It throws an error incorrectly because !num is true for 0 -> Option A
Quick Check:
Falsy check fails for 0, use isNaN instead [OK]

Quick Trick: Falsy check fails for 0; use isNaN() to validate numbers [OK]

Common Mistakes:

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