Chapter 8: Functions

Question 1

Example function

Answer 1

// Print the name and value of each property of o. Return
undefined.
function printprops(o) {
for(let p in o) {
console.log(${p}: ${o[p]}\n);

Question 2

Function expression

Answer 2

/ This function expression defines a function that squares
its argument.
// Note that we assign it to a variable
const square = function(x) { return xx; };
// Function expressions can include names, which is useful
for recursion.
const f = function fact(x) { if (x <= 1) return 1; else
return xfact(x-1); };

Question 3

Arrow function example

Answer 3

const sum = (x, y) => x + y;

Question 4

Furthermore, if an arrow function has exactly one parameter, you can
omit the parentheses around the _______ ____

Answer 4

parameter list

const polynomial = x => xx + 2x + 3;

Question 5

Arrow functions differ from functions defined in other ways in one
critical way: they inherit the value of the ____ keyword from the
environment in which they are defined rather than defining their own
invocation context as functions defined in other ways do

Answer 5

this

Question 6

In JavaScript, functions may be nested within other functions

Answer 6

True

Question 7

Functions written to be invoked as functions (and not as methods) do
not typically use the ____ keyword at all.

Answer 7

this

Question 8

o“m”; // Another way to write o.m(x,y).
a0 // Also a method invocation (assuming a[0] is
a function).

Answer 8

Other examples of method invocation

Question 9

customer.surname.toUpperCase(); // Invoke method on
customer.surname
f().m(); // Invoke method m() on
return value of f()

Answer 9

Other examples of method invocation

Question 10

If a function or method invocation is preceded by the keyword _____,
then it is a constructor invocation

Answer 10

new

Question 11

JavaScript method parameters have no ______ _____, and no type
checking is performed on the values you pass to a function

Answer 11

declared types

Question 12

In JavaScript,
however, functions are not only syntax but also values, which means
they can be assigned to variables, stored in the properties of objects or
the elements of arrays, passed as arguments to functions

Answer 12

True

Question 13

Functions can also be assigned to ____ properties rather than
variables. As we’ve already discussed, we call the functions “methods”
when we do this

Answer 13

object

let o = {square: function(x) { return x*x; }}; // An object
literal
let y = o.square(16);

Question 14

JavaScript
functions are executed using the ______ they were defined in. The
nested function f() was defined in a scope where the variable scope
was bound to the value “local scope”. That binding is still in effect
when f is executed, no matter where it is executed from

Answer 14

scope

Question 15

let scope = “global scope”; // A global variable
function checkscope() {
let scope = “local scope”; // A local variable
function f() { return scope; } // Return the value in
scope here
return f;
}
let s = checkscope()(); // What does this
return?

Answer 15

“local scope”

Question 16

// Return an array of functions that return the values 0-9
function constfuncs() {
let funcs = [];
for(var i = 0; i < 10; i++) {
funcs[i] = () => i;
}
return funcs;
}
let funcs = constfuncs();
funcs5 // => 10; Why doesn’t this return 5?

Answer 16

Returns 10 because the value of variable i at the end of the for loop is 10 so all 10 closures share this value

Question 17

All functions, except arrow functions, have a _______ property
that refers to an object known as the prototype object

Answer 17

prototype

Question 18

The primary purpose of _____ is to bind a function to an object

Answer 18

bind()

Question 19

Function constructor

Answer 19

const f = new Function(“x”, “y”, “return x*y;”);

Question 20

The ______ function in JavaScript is used to create a new function with a specific this value and optional preset arguments

It’s commonly used when you want to control what this refers to

Answer 20

bind()