3 - Functions

Question 1

What purposes do functions serve?

Answer 1

1. reduce repetition
2. enable naming concepts (abstractions)
3. isolate code
4. design and sturcture programs

Question 2

What is a function definition?

Answer 2

A binding that references a function value.

Question 3

What construct enables a function to receive input?

Answer 3

Parameters.

Question 4

What is a function argument?

Answer 4

Value that is bind to a function parameter when the function is called.

Question 5

What is a function body?

Answer 5

Block of code which wraps code of a function.

Question 6

How many params can a function have?

Answer 6

There is no limit on the number of params function can take.

Question 7

What happens when function defines one param, but is passed two?

Answer 7

Additional parameters are ignored.

Question 8

Why can’t a function be called with more parameters then the amount of the ones you define?

Answer 8

It can.

Question 9

When you invoke a function with lesser number of arguments than those defined, what happens?

Answer 9

Params which don’t receive a value on invocation are assigned ‘undefined’.

Question 10

What is the minimal number of arguments you can define a function with?

Answer 10

Zero.

Question 11

What are the ways to define a function?

Answer 11

1. function foo() {}
2. const foo = function() {}
3. const foo = () => {}

Question 12

For which two things you use functions for?

Answer 12

1. return a value
2. side effect

Question 13

What keyword do you use inside a function to return a value?

Answer 13

‘return’

Question 14

What is the return value when there is no ‘return’ statement in the function?

Answer 14

‘undefined’

Question 15

What happens when you return two values in a list ‘return 1, 2;’?

Answer 15

Returned value is ‘2’.

Question 16

What is the anatomy of a function?

Answer 16

1. might have ‘function’ keyword
2. name of a function
3. parameters
4. body

Question 17

When you pass an array to a function, how do you assign its elements to different arguments?

Answer 17

Destructuring an array in the params. (function foo([a, b]))

Question 18

How is a top-level scope called?

Answer 18

Global scope.

Question 19

Which type of binding leaks out of a code block scope?

Answer 19

var

Question 20

Which type of binding is limited to the scope of the code block?

Answer 20

let/const

Question 21

What is the name of a scope created by a function?

Answer 21

Local.

Question 22

Why can you reference binding defined in the local (child) scope in the parent scope?

Answer 22

You can’t.

Question 23

If a function is defined in the global scope, where can you create a binding and have it available in the local scope of a function?

Answer 23

Global and local scope. Both will be available in the local scope.

Question 24

Does lexical scoping imply which bindings in the outer scope are visible in the local scopes, or the other way around?

Answer 24

It means that bindings defined in outer scopes are available in the nested (local) scopes.

Question 25

What is scope locality?

Answer 25

Degree of scope nesting.

Question 26

How deep can local scopes be nested?

Answer 26

Until stack overflow.

Question 27

What does it mean that a function is a value? How is it different from other languages?

Answer 27

1) it can be returned as a value of another function
2) it can be passed as a parameter to another function

Question 28

How do you write a function declaration?

Answer 28

‘function foo() {}’

Question 29

Why is function declaration different than assigning a function value to a binding?

Answer 29

Its binding can be used in the program before the location of the function declaration - hoisting.

Question 30

When defining arrow function, in which instances can you leave out parantheses?

Answer 30

When the function has one param.

Question 31

When defining arrow function, in which instances do you have to use parantheses?

Answer 31

1) when it doesn’t have any params
2) when it has two, or more, params

Question 32

When are you allowed to omit braces in the arrow function declaration?

Answer 32

When it is defined on a single line.

Question 33

Why do you have to use ‘return’ keyword when you define an arrow function on a single line?

Answer 33

You don’t.

Question 34

When defining arrow function on multiple lines how do you return a value?

Answer 34

With ‘return’ keyword.

Question 35

Why have arrow functions been added to the language?

Answer 35

Because it is convenient to write them when passing them inline as values.

Question 35

What is needed for a JS engine to be able to jump back and forth between different scopes?

Answer 35

Stack which is persisted in the computer memory.

Question 35

What is the flow of control here?

function greet(who) {
console.log(who);
}
greet(‘Harry’);
console.log(‘Hi’);

Answer 35

not in function
in greet
in console.log
in greet
not in function
in console.log
not in function

Question 36

How is the stack in which JS engine persists scopes/function calls called?

Answer 36

Call stack.

Question 37

What is stack overflow?

Answer 37

An event where the memory of the call stack is full, but the program continues to add new contexts to it, resulting in an error.

Question 38

How can you intentionally blow up a stack?

Answer 38

1) calling a function recursively without a return
2) writing a circular reference
3) writing an infinite loop

Question 39

How do you define an optional parameter?

Answer 39

By writing ‘=’ after a param and assigning it a default value.

Question 40

What happens when function takes one optional parameter but is passed a value when invoked?

Answer 40

The parameter is bind to the passed value.