Functions

Question 1

What is the invocation context of a function ?

Answer 1

It is the value of the ‘this’ keyword.
Usually, when a function that is a property of an object is invoked on (or through) this object, that object is the invocation context or the ‘this’ value for the function.

Question 2

Javascript functions are closures. What does it mean ?

Answer 2

It mean that javascript functions can be nested within other functions, and they have access to any variables that are in scope where there are defined.

Question 3

What are the different ways to create functions in javascript ?

Answer 3

• Using the function keyword either as a declaration or as an expression
• Using the shorthand syntax (arrow functions)
• In object litterals and class definitions, using the shorthand syntax for declaring methods. As well as getters and setters.
• Using the Function constructor
• Using specialized kind of functions as : generators (function*) and async functions.

Question 4

What does the following mean: Function declarations are hoisted ?

Answer 4

Function declarations are hoisted to the top of the enclosing script, function or block so that functions defined in this way may be invoked from code that appear before the definition.

It means that all of the function declared in a block of javascript code will be defined throughout that block, and they will be defined before the javascript interpreter begins to execute any of the code in that block.

Question 5

Functions are objects.
True or False ?

Answer 5

True

Question 6

What is a function in JavaScript?

Answer 6

A block of JavaScript code that is defined once but may be executed any number of times.

Question 7

What are parameters in a JavaScript function?

Answer 7

Identifiers that work as local variables for the body of the function.

Question 8

What are arguments in a function invocation?

Answer 8

Values provided to a function’s parameters during invocation.

Question 9

What is the return value of a function?

Answer 9

The value computed by the function using its argument values.

Question 10

What does the ‘this’ keyword represent in a function invocation?

Answer 10

The invocation context of the function.

Question 11

What is a method in JavaScript?

Answer 11

A function assigned to a property of an object.

Question 12

What are constructors in JavaScript?

Answer 12

Functions designed to initialize a newly created object.

Question 13

How are JavaScript functions treated in the language?

Answer 13

JavaScript functions are objects and can be manipulated by programs.

Question 14

What is a closure in JavaScript?

Answer 14

A function that has access to its own scope, the outer function’s scope, and the global scope.

Question 15

What is the most straightforward way to define a JavaScript function?

Answer 15

Using the function keyword.

Question 16

What are arrow functions in JavaScript?

Answer 16

A compact syntax for defining functions introduced in ES6, using the => syntax.

Question 17

What is the syntax for a function declaration?

Answer 17

function keyword, followed by an identifier, parentheses with parameters, and curly braces with statements.

Question 18

What is hoisting in JavaScript functions?

Answer 18

Function declaration statements are moved to the top of their enclosing block, allowing them to be invoked before their definition.

Question 19

What happens if a function does not contain a return statement?

Answer 19

It executes until the end and returns undefined.

Question 20

True or False: In ES6, function declarations are only allowed at the top level.

Answer 20

False.

Question 21

What is the difference between function declarations and function expressions?

Answer 21

Declarations are hoisted and can be called before their definition; expressions are not hoisted.

Question 22

Fill in the blank: Arrow functions use the _______ syntax to separate parameters from the function body.

Answer 22

=>

Question 23

What must be included when returning an object literal from an arrow function?

Answer 23

The object literal must be inside parentheses.

Question 24

What is the significance of the ‘this’ keyword in arrow functions?

Answer 24

Arrow functions inherit the value of ‘this’ from the surrounding context.

Question 25

What is a nested function in JavaScript?

Answer 25

A function defined within another function.

Question 26

How do nested functions access variables?

Answer 26

They can access parameters and variables of the outer function.

Question 29

What is a nested function?

Answer 29

A nested function is simply a function defined inside another function.

Question 30

Provide an example of a nested function.

Answer 30

function outer() { function inner() { console.log("I'm nested!"); } inner(); }

Question 31

What is a closure?

Answer 31

A closure is a function that remembers and has access to variables from the scope in which it was defined, even after that scope has exited.

Question 32

Provide an example of a closure.

Answer 32

function outer() { let count = 0; return function inner() { count++; console.log(count); } } const counter = outer(); counter(); // 1 counter(); // 2

Question 33

What is the key difference between a nested function and a closure?

Answer 33

All closures are nested functions, but not all nested functions are closures.

Question 34

When does a nested function become a closure?

Answer 34

A nested function becomes a closure only when it accesses variables from its outer scope after the outer function has returned.

Question 35

True or False: All nested functions are closures.

Answer 35

False

Question 36

True or False: A closure is a structural concept.

Answer 36

False

Question 37

Fill in the blank: A nested function is a function defined ______ another function.

Answer 37

inside

Question 38

Fill in the blank: A closure is a function that remembers and has access to variables from the ______ in which it was defined.

Answer 38

scope

Question 39

What does a closure allow a function to do after the outer function has returned?

Answer 39

Access variables from the outer function's scope.

Question 40

What determines the value of `this` inside a regular function in JavaScript?

Answer 40

How the function is called

Question 41

How do arrow functions handle the value of `this`?

Answer 41

They inherit the `this` value from the environment in which they were defined

Question 42

What is the term for the way arrow functions handle `this`?

Answer 42

Lexical scoping

Question 43

In the example of a regular function, what does `this` refer to when calling `person.greet()`?

Answer 43

The object `person`

Question 44

What happens when a regular function is called without an object context?

Answer 44

This becomes the global object, so `this.name` is undefined

Question 45

What will `person.greet()` output if `greet` is defined as an arrow function?

Answer 45

Hi, I'm undefined

Question 46

Why does `this` not refer to `person` in the arrow function example?

Answer 46

Because the arrow function inherits `this` from its surrounding context

Question 47

What is a typical use case for arrow functions?

Answer 47

Callbacks, especially in classes or objects where you want `this` to refer to the enclosing object

Question 48

In the `Timer` example, what does `this` refer to when using an arrow function in `setInterval`?

Answer 48

The Timer instance

Question 49

Can arrow functions be used as constructors?

Answer 49

No

Question 50

What will happen if you try to use an arrow function with `new`?

Answer 50

TypeError: Person is not a constructor

Question 51

What is a key difference between regular functions and arrow functions regarding `prototype`?

Answer 51

Regular functions have a `prototype`, arrow functions do not

Question 52

Fill in the blank: Arrow functions are mostly used for _______ and _______.

Answer 52

small functions and callbacks

Question 53

True or False: Arrow functions are good for methods.

Answer 53

False

Question 54

What output does the `Timer` example produce every second?

Answer 54

1, 2, 3, 4...

Question 55

What is the main advantage of using arrow functions in callbacks?

Answer 55

They provide lexical `this`

Question 56

In the summary table, which type of function is good for methods?

Answer 56

Regular Function

Question 57

In the summary table, which type of function is marked as usually not good for methods?

Answer 57

Arrow Function

Question 60

What does `this` refer to in JavaScript?

Answer 60

`this` refers to the execution context — the object that is currently executing the function.

Question 61

What does `this` refer to in the global context (outside any function or class)?

Answer 61

In browsers: `window`, in Node.js: `global`.

Question 62

What is the value of `this` inside a non-strict mode function?

Answer 62

In browsers: `window`.

Question 63

What is the value of `this` inside a strict mode function?

Answer 63

`undefined`.

Question 64

What does `this` refer to inside an object method?

Answer 64

The object the method was called on.

Question 65

What happens to `this` in arrow functions?

Answer 65

Arrow functions do not bind their own `this`, they inherit it from their lexical scope.

Question 66

What does `this` refer to when using a constructor function?

Answer 66

The newly created object.

Question 67

What does `this` refer to inside a class method?

Answer 67

The instance of the class.

Question 68

What do the methods call(), apply(), and bind() do in relation to `this`?

Answer 68

They let you manually control what `this` points to.

Question 69

What is the difference between call() and apply()?

Answer 69

Both immediately invoke the function with `this` set to the first argument, but apply() takes an array of arguments.

Question 70

What does `this` refer to in a regular function inside setTimeout?

Answer 70

Global object (in browsers).

Question 71

What does `this` refer to in an event handler using a regular function?

Answer 71

The DOM element triggering the event.

Question 72

What does `this` refer to in an event handler using an arrow function?

Answer 72

Lexical `this`, often `window`.

Question 73

Fill in the blank: When a function is used with ______, `this` refers to the newly created object.

Answer 73

[new]

Question 74

True or False: In strict mode, `this` is always `undefined`.

Answer 74

False.

Question 75

What is the value of `this` in a DOM inline event handler?

Answer 75

The button element.

Question 76

List the contexts and their corresponding `this` values from the summary table.

Answer 76

* Global scope (non-strict): Global object (window or global) * Global scope (strict mode): undefined * Inside a method: The object the method was called on * Inside a regular function: Depends on call site * Inside a constructor: The newly created object * Inside an arrow function: Inherits from enclosing scope * With call, apply, or bind: The explicitly provided object * In event handler (regular func): The DOM element triggering the event * In event handler (arrow func): Lexical this, often window * In setTimeout / setInterval: Global object unless arrow function * Inside class methods: The instance of the class.

Question 77

What are nested functions in JavaScript?

Answer 77

Functions that are defined within other functions.

Question 78

What can nested functions access?

Answer 78

Parameters and variables of the function they are nested within.

Question 79

When is the body of a JavaScript function executed?

Answer 79

When the function is invoked.

Question 80

How many ways can JavaScript functions be invoked?

Answer 80

Five ways: * As functions * As methods * As constructors * Indirectly with call() and apply() * Implicitly via language features.

Question 81

What is an invocation expression in JavaScript?

Answer 81

A function expression followed by parentheses containing arguments.

Question 82

What happens to argument expressions in a function invocation?

Answer 82

They are evaluated and the resulting values become the arguments to the function.

Question 83

What is the return value of a function invocation if it reaches the end without a return statement?

Answer 83

Undefined.

Question 84

What does the syntax f?.(x) do in JavaScript?

Answer 84

Invokes the function only if it is not null or undefined.

Question 85

What is the invocation context in non-strict mode?

Answer 85

The global object.

Question 86

What is a recursive function?

Answer 86

A function that calls itself.

Question 87

What is the stack in relation to recursive functions?

Answer 87

A structure that keeps track of execution contexts for each function call.

Question 88

What does a method in JavaScript refer to?

Answer 88

A function stored in a property of an object.

Question 89

How is a method invoked?

Answer 89

Using the syntax o.m(); where o is the object and m is the method.

Question 90

What is the significance of the this keyword in method invocations?

Answer 90

It refers to the object through which the method is invoked.

Question 91

What is method chaining?

Answer 91

Invoking multiple methods on the same object in a single expression.

Question 92

What does the keyword new signify in a function invocation?

Answer 92

It indicates a constructor invocation.

Question 93

What is a constructor function's typical behavior regarding return values?

Answer 93

It initializes a new object and returns it implicitly.

Question 94

What is the purpose of the call() and apply() methods in JavaScript?

Answer 94

To invoke a function indirectly and specify the this value.

Question 95

What can cause implicit function invocations in JavaScript?

Answer 95

Features like getters/setters, toString(), valueOf(), iterables, and tagged template literals.

Question 96

True or False: Functions defined as expressions are hoisted.

Answer 96

False.

Question 97

Fill in the blank: A _______ function is one that calls itself.

Answer 97

recursive