Angular - Reactive Forms
Why should a custom validator function in Angular always return null when the input is valid instead of undefined or other values?
Why should a custom validator function in Angular always return null when the input is valid instead of undefined or other values?
hard🧠 Conceptual Q10 of 15
Step-by-Step Solution
Solution:
Step 1: Understand Angular validation contract
Angular expects validators to return null if valid, or an error object if invalid.Step 2: Effect of return values
Returning null signals no error; any other value (including undefined) is treated as an error.Final Answer:
Because Angular treats null as no error and any other value as an error -> Option CQuick Check:
Return null for valid input to avoid errors [OK]
Quick Trick: Return null for valid input, anything else signals error [OK]
Common Mistakes:
MISTAKES- Returning undefined and expecting valid
- Returning empty object instead of null
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