[Solved] You have an interface Person with optional property middleName?. How would you correctly declare it?Choose the correct interface declaration: | Angular

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You have an interface Person with optional property middleName?. How would you correctly declare it?

Choose the correct interface declaration:

Ainterface Person { firstName: string; middleName?: string; lastName: string; }

Binterface Person { firstName: string; middleName: string; lastName: string; }

Cinterface Person { firstName: string; middleName: optional string; lastName: string; }

Dinterface Person { firstName: string; middleName: string | undefined; lastName: string; }

Step-by-Step Solution

Solution:

Step 1: Understand optional properties syntax
Optional properties use a question mark after the name, like middleName?: string;.
Step 2: Compare options
interface Person { firstName: string; middleName?: string; lastName: string; } correctly uses the question mark. interface Person { firstName: string; middleName: string; lastName: string; } makes it required. interface Person { firstName: string; middleName: optional string; lastName: string; } uses invalid syntax. interface Person { firstName: string; middleName: string | undefined; lastName: string; } uses a union but is not the standard optional syntax.
Final Answer:
interface Person { firstName: string; middleName?: string; lastName: string; } -> Option A
Quick Check:
Optional property syntax = question mark [OK]

Quick Trick: Use '?' after property name to mark it optional [OK]

Common Mistakes:

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You have an interface Person with optional property middleName?. How would you correctly declare it?