Arrow Functions: Scope u0026 Behavior Quiz Quiz

Explore the nuances of arrow functions in JavaScript, focusing on their unique handling of scope and binding behavior. Assess your understanding of how arrow functions differ from traditional functions in various coding contexts.

1. Lexical 'this' Binding

   When using an arrow function as a method inside an object, such as const obj = { value: 5, getValue: () =u003E this.value }, what will obj.getValue() return?

   1. undefined
   2. 5
   3. Error
   4. null

   Explanation: Arrow functions do not have their own 'this' context; instead, they inherit 'this' from their lexical scope, which in this case is the global object or undefined in strict mode. That's why obj.getValue() returns undefined. If a regular function was used, it would return 5 since 'this' refers to the object. 'null' and 'Error' are incorrect, as no exception is thrown and the value does not become null.

2. Arrow Functions as Constructors

   What happens if you attempt to use an arrow function as a constructor with the 'new' keyword, for example: const Foo = () =u003E {}; const bar = new Foo();?

   1. It returns undefined
   2. It sets the object prototype to null
   3. It throws a TypeError
   4. It creates an empty object

   Explanation: Arrow functions cannot be used as constructors and will throw a TypeError if used with 'new'. Regular functions, unlike arrow functions, have a [[Construct]] method, enabling their use with 'new'. The options claiming it creates an object, returns undefined, or sets prototype to null are all incorrect because no instance is created at all.

3. Arguments Object in Arrow Functions

   Given function example() { return (() =u003E arguments[0])('b'); }, what does example('a') return?

   1. undefined
   2. An error
   3. 'a'
   4. 'b'

   Explanation: An arrow function does not have its own 'arguments' object; it inherits one from the containing function, in this case, example. Therefore, arguments[0] refers to the first argument passed to example, which is 'a'. 'b' is incorrect because it is passed to the arrow function, not to example. 'undefined' and 'An error' are incorrect since the code executes and resolves correctly.

4. Implicit Return in Arrow Functions

   What is the value of result in the following: const result = (() =u003E { name: 'quiz' })(); ?

   1. An error
   2. { name: 'quiz' }
   3. null
   4. undefined

   Explanation: When using curly braces in an arrow function, they signify a function body, not an object literal. Without a return statement, undefined is returned. Option '{ name: 'quiz' }' is not correct because returning an object literal requires parentheses around it. Choices 'null' and 'An error' are inaccurate, as no error is thrown and nothing is set to null.

5. Arrow Functions in Event Handlers

   If you define an event handler as element.onclick = () =u003E { this.doSomething(); }, what does 'this' refer to inside the arrow function?

   1. The enclosing lexical scope
   2. The global event object
   3. The element triggering the event
   4. The prototype of the element

   Explanation: Arrow functions do not have their own 'this'; they capture the value from their enclosing lexical context. This means 'this' may not point to the element that triggered the event, making them less suitable as event handlers when 'this' is needed. The element itself (option 2) would be correct for traditional functions, but not for arrow functions. The event object and the element's prototype are unrelated.