Vue with TypeScript: Strong Typing for Components Quiz Quiz

Challenge your understanding of implementing strong typing in Vue components using TypeScript. Assess your knowledge on typing props, methods, emits, and component options for robust type safety and cleaner code in modern JavaScript applications.

1. Typing Props Correctly

   When defining a Vue component in TypeScript, which is the most type-safe way to specify the prop 'count' as a required number with default value 10?

   1. props: { count: Number }
   2. props: { count: String, default: '10' }
   3. props: { count: { required: true } }
   4. props: { count: { type: Number, required: true, default: 10 } }

   Explanation: The correct answer explicitly types the prop as a number, requires it, and sets a default value, ensuring clarity and strong typing for the prop. Option two lacks 'required' and 'default' settings, limiting type safety. Option three incorrectly assigns a string type and string default, which violates the intended numeric type. Option four fails to specify a type, making the prop's expected value ambiguous and weakening type safety.

2. Typing Component Methods

   Which approach best enforces type safety for a method 'increment' that takes a number and returns nothing in a Vue component using TypeScript?

   1. increment(amount) { this.count += amount; }
   2. increment(amount: number): void { this.count += amount; }
   3. increment = function(amount: number): string { this.count += amount; return ''; }
   4. increment(amount: string): any { this.count += parseInt(amount); }

   Explanation: Defining 'increment' with both parameter and return types ensures that only numbers are accepted and nothing is returned, providing strong type safety. Option two omits all typing, leading to potential runtime errors. Option three expects a string and returns any type, which is risky and less type-strict. Option four enforces a string return type, which does not match the intended use, and its function expression syntax is less common in component definitions.

3. Typing Emits with TypeScript

   How should you type a Vue event emit named 'update' that expects a boolean payload when using TypeScript with the Options API?

   1. emits: { update: Boolean }
   2. emits: { update: (payload: number) =u003E true }
   3. emits: { update: (payload: boolean) =u003E true }
   4. emits: ['update']

   Explanation: This pattern ensures that the 'update' emit event only accepts boolean payloads by validating the argument's type. Option two does not provide any payload type checking, reducing type safety. Option three incorrectly uses a type directly instead of a validator function, which is not sufficient for TypeScript type enforcement. Option four is typed for numbers, not booleans, so it does not match the expected payload type.

4. Type Safety with Reactive Data

   When using 'ref' in a Vue component with TypeScript, what is the correct way to declare a reactive variable 'message' of type string?

   1. const message: string = ref('Hello');
   2. let message = refu003Cnumberu003E(123);
   3. const message = ref('Hello');
   4. const message = refu003Cstringu003E('Hello');

   Explanation: Using 'ref' with a generic parameter 'u003Cstringu003E' enforces that 'message.value' will always be a string, ensuring type safety. Option two incorrectly assigns a ref to a non-ref-typed variable, which does not provide proper Reactivity or type safety. Option three is valid if TypeScript infers the type, but for explicit typing, the correct syntax is best. Option four uses a number type and does not match the intended string use.

5. Strong Typing for Computed Properties

   Which method best strongly types a computed property 'fullName' in TypeScript that combines two string properties, 'firstName' and 'lastName'?

   1. const fullName = computed(() =u003E firstName + lastName);
   2. const fullName: string = computed(() =u003E `${firstName.value} ${lastName.value}`);
   3. computed = function() { return firstName.value + lastName.value; }
   4. const fullName = computedu003Cstringu003E(() =u003E firstName.value + ' ' + lastName.value);

   Explanation: Providing a generic 'u003Cstringu003E' to computed explicitly types its result, ensuring 'fullName' is recognized as a string by TypeScript. Option two does not specify types and potentially concatenates reactive objects directly, which may not yield strings. Option three mistakenly tries to assign the computed ref directly to a string, which is a type mismatch. Option four uses an unrelated function declaration, lacking context for compute reactivity and type annotation.