LIS2360 lesson 6

Write the code to display "You are X", where X is the value of the age variable. age = 21; console.log(_________);

"You are " + age

non-identity operator

!== is the opposite of the identity operator

anonymous function

a function that does not have a name

method

a function that is attached to an object and operates on data stored in the object

console

a location where text output is displayed

infinite loop

a loop that never stops executing

while loop

a looping structure that checks if the loop's condition is true before executing the loop body, repeating until the condition is false

A JavaScript coding convention is to name JavaScript variables with camel casing, where the identifier starts with

a lowercase letter, and subsequent words begin with a capital letter. Ex: lastPrice

indentifier

a name created by a programmer for an item like a variable or function

function

a named group of statements

truthy

a non-Boolean value that evaluates to true in a Boolean context

let

a variable can be declare with let

local scope

a variable declared inside a function the function that defines the variable has access to the local variable

global scope

a variable declared outside a function all functions have access to a global variable

What is output to the console? ar autos = ["Chevrolet", "Dodge", "Ford", "Ram"]; for (i = 0; i < autos.length; i++) { if (i % 2 == 0) { console.log(autos[i]); } }

chevrolet, ford (only elemnets with even indexes are printed)

What is output to the console? var autos = ["Chevrolet", "Dodge", "Ford", "Ram"]; autos.forEach(function(item, index) { if (index % 3 == 0) { console.log(item); } });

chevrolet, ram (only elements with indexes that are evenly divisible by 3 are output)

compound assignment operator

combines an assignment statement with an arithmetic operation

switch statement

compares an expression's value to several cases using strict equality (===) and executes the first matching case's statements

length

contains the number of elements in the array

parseInt() and parseFloat()

convert strings into numbers

NaN

convert strings into numbers isNaN() returns true if the argument is not a number, false otherwise

Which identifier is illegally named? a. star_destroyer b. ADDRESS c. $save d. 9to5

d. 9to5

object

data type collection of property and value pairs

string

data type group of characters delimited with 'single' or "double" quotes

null

data type intentionally absent of any object value

array

data type list of items

numbers

data type numbers with or without decimal places

boolean

data type true or false

undefined

data type variable without a value

array object

defines numerous methods for manipulating arrays

dynamic typing

determines a variable's type at run-time

console.log() function

displays text or numbers in the console

Which loop always executes the loop body at least once?

do-while loop

JavaScript engines

modern JavaScript interpreters

x = 10; var y = 20;

no error

Write the function call to display the question variable to the user and retrieve the user's age. question = "How old are you?"; age = __________;

prompt(question)

prompt() function

prompts the user with a dialog box that allows the user to type a single line of text and press OK or Cancel and returns the string the user typed or null if the user pressed Cancel

shift()

removes the first array element and returns the element

pop()

removes the last array element and returns the element

indexOf() and lastIndexOf()

search an array and return the index of the first found value or -1 if the value is not found indexOf() searches beginning to end, lastINdexOf() searches end to beginning

for-of

statement is a simplified for loop that loops through an entire array

break statement

stops executing a case's statements and causes the statement immediately following the switch statement to execute

scope

the context in which the variable can be accessed

ECMAScript

the standard that has been improved over the years, and JavaScript is an implementation of ECMAScript. The latest version of ECMAScript is version 9 (ES9) and was released in 2018

loop body

the statements that a loop repeatedly executes

block scope

the variable is accessible only within the enclosing pair of curly braces

artists.indexOf("Botticelli") returns 3. var artists = ["Raphael", "Titian", "Masaccio", "Botticelli", "Titian"];

true

if (" ")

true

if (999)

true

if (myArray)

true

Array elements that are not assigned a value are

undefined

just-in-time (JIT) compilation

used by JavaScript engines to compile the JavaScript code at execution time into another format that can be executed quickly.

elements

values in an array

What is missing in the for-of loop to display all the elements in the autos array? var autos = ["Chevrolet", "Dodge", "Ford", "Ram"]; for (____) { console.log(auto); }

var auto of autos (each array element in autos is assigned to the auto variable, which is logged to the console)

What is autos.length? var autos = ["Chevrolet", "Dodge", "Ford", "Ram"];

4

What numbers are output by the code segment? for (c = 5; c < 10; c +=2;) { console.log(c);

5,7,9

identity operator

=== performs strict equality two operands are strictly equal if the operands' data types and values are equal

JavaScript background

Brendan Eich created JavaScript in 1995 so the Netscape Navigator browser could dynamically respond to user events JavaScript was standardized by Ecma International in 1997 and called ECMAScript

hoisting

JavaScript's behavior of moving variable declarations to the top of the current scope

What is syntactically wrong with the following code? name = 'Danny O'Sullivan' a. name is assigned a value without being declared first b. variables may not be assigned strings delimited with single quotes c. the single quotation mark in O'Sullivan

c. the single quotation mark in O'Sullivan

Which variable is named with the preferred JavaScript naming conventions? a. total_points b. $totalPoints c. totalPoints

c. totalPoints

continue

causes a loop to iterate again without executing the remaining statements in the loop

What is output to the console? var autos = ["Chevrolet", "Dodge", "Ford", "Ram"]; for (i = 0; i < 2; i++) { console.log(autos[i]); }

chevrolet, dodge

What is the data type of z? var = z; a. undefined b. string c. number

a. undefined

unshift(value)

adds a value to the beginning of the array

push(value)

adds a value to the end of the array

splice(startingIndex, totalElementsToDelete, valuesToAdd)

adds or removes elements from anywhere in the array and returns the deleted elements (if any)

forEach()

also loops through an array method takes a function as an argument

arrow function

an anonymous function that uses an arrow => to create a compact function

constant

an initialized variable whose value cannot change usually named with an identifier in all capital letters keyword: const

global object

an object that stores certain global variables, functions, and other properties

array

an ordered collection of values

comment

any text intended for humans that is ignored by the JavaScript interpreter

string concatenation

appends one string after the end of another string, forming a single string

What is the data type of x? y = false; x = y; a. string b. boolean c. number

b. boolean

Which statement declares a constant for Earth's gravity? a. var EARTH_GRAVITY = 9.8; b. const EARTH_GRAVITY = 9.8; c. const EARTH_GRAVITY;

b. const EARTH_GRAVITY = 9.8;

Which statement declares the variable sum without assigning a value to sum? a. sum; b. var sum; c. sum=0;

b. var sum;

break

breaks out of a loop prematurely

Which condition causes the for loop to output the numbers 100 down to 50, inclusively? for (c = 100; ____________; c--;) { console.log(c);

c >=50

index

each array element is stored in a numeric location

/* a is assigned 2 a = 2;

error

3.12 = pi;

error

if-else statement

executes a block of statements if the statement's condition is true, and optionally executes another block of statements if the condition is false

interpreter

executes programming statements without first compiling the statements into machine language

for-loop

executes the initialization expression, evaluates the loop's condition, and executes the loop body if the condition is true

do-while loop

executes the loop body before checking the loop's condition to determine if the loop should execute again, repeating until the condition is false

All browsers must use the same JavaScript engine

false

ECMAScript and JavaScript are the same thing

false

JavaScript and Java are the same programming language

false

JavaScript is only used for programs that run in a web browser

false

if ("")

false

if (0)

false

if (NaN)

false

if (undefined)

false

Which loop is best for looping through an array in reverse order (from last element to first element)?

for loop (the for-of and forEach() loops always loop through an array starting with the first element and ending at the last element.) the for loop provides more control than the other loops over the order in which array elements are accessed

conditional operator

has three operands

function expression

identical to a function declaration, except the function name is omitted

variable

is a named container that stores a value does not have to be declared before being assigned a value keyword: var

falsy

is a non-Boolean value that evaluates to false in a Boolean context

self-invoking function

is an anonymous function that invokes (calls) itself