YDKJS Up and Going

Question 1

How do you quickly retrieve input in a browser popup?

Answer 1

const answer = prompt('Type answer');

Question 2

What are objects?

Answer 2

Values that hold other values at specific named locations called properties.

Question 3

A block is…

Answer 3

one or more statements wrapped inside a curly-brace pair {...}

Question 4

An iteration is..

Answer 4

each time a loop block executes.

Question 5

You can stop a loop with..

Answer 5

the break statement

Question 6

Each function gets its own..

Answer 6

scope

Question 7

Lexical scope rules say that one scope can access variables of…

Answer 7

…either that scope or any scope outside (not inside) it

Question 8

The built-in types are…

Answer 8

6 primitives:

• string
• number
• boolean
• null
• undefined
• symbol (new in ES6)

and object

Question 9

Use ____ to tell you the type of a value currently in variable

Answer 9

typeof variable

Question 10

Variables can get to the undefined state from…

Answer 10

• functions that have no return value
• the void operator

Question 11

typeof returns

Answer 11

• function type, a subtype of object
• implying it can have properties, although this won’t be used often

Question 12

Object wrappers that pair with their primitive type and define method swhich go on its prototype are called…

Answer 12

natives.

string value -> String object

number value -> Number object

so on for all primitives that have properties and methods

Question 13

When using a primitive value as an object by referencing a property or method…

Answer 13

JS automatically “boxes” the value in its object wrapper to enable the use of properties and methods.

Question 14

All “falsy” values are:

Answer 14

• ""
• 0, -0, Nan
• null, undefined
• false

Question 15

Examples of “truthy” values are:

Answer 15

• "hello"
• 42
• true
• [], [1, 2, 3]
• {}, {a: 42}
• function foo() {...}

Question 16

What is the difference between == and ===?

Answer 16

• == checks for value equality with coersion allowed
• === checks for value equality without coercsion allowed

Question 17

During inequality operations, if one or both values is not a string…

Answer 17

’

…then both values are coerced to be a number, and then compared.

Question 18

Variables must be a valid ______ (which must begin with ___ )

Answer 18

identifier….any letter, $, or _

Question 19

The var keyword declares a variable that will belong to…

Answer 19

the current function scope, or global scope if at the top level outside of any function

Question 20

var and hoisting

Answer 20

• a var declaration is hoisted to the top of its enclosing scope so that it can be accessible anywhere in the scope
• the value assignment is not hoised, just the declaration

Question 21

Trying to access a variable’s value in a scope where it’s not available will cause…

Answer 21

…a ReferenceError to be thrown

Question 22

the let keywords enables you to declare variables…

Answer 22

that belong to individual blocks, contained within curly-braces {...}

Question 23

In a switch statement, you must use _____ if you only want one case to run, otherwise it will ‘fallthrough’ to other matching cases

Answer 23

break

Question 24

Strict mode disallows….

Answer 24

implicit auto-global variable declaration from omitting var

Question 25

`var x = function bar() { // ..};` is ...

Answer 25

...a named function expression

Question 26

`var x = function() { // ..};` is...

Answer 26

an anonymous function expression

Question 27

`(function() { // ..})();` is...

Answer 27

* ...an immediately invoked function expression (IIFE) * outer `(...)` treats it as a function expression instead of function declaration * the final `()` executes the function

Question 28

Closures are a way to...

Answer 28

"remember" and *continue to access* a function's scope (its variables), *even once* the function has finished running

Question 29

The module pattern returns...

Answer 29

...an object that references functions which will remember and continue to access their scope

Question 30

`this` gets set in one of these four ways...

Answer 30

* from the global object * an object on which it is called from * an object from which it is called by way of `call` or `apply` * a blank object if using `new ()`

Question 31

Prototype Lookup

Answer 31

If referencing a property on an object, and it doesn't exist, JavaScript will automatically use the object's internal prototype reference to find another object to look for the property on

Question 32

Transpiling is

Answer 32

converting newer code into older code equivalent

Question 33

`document` is a special object that exists as a global variable and is called a...

Answer 33

"host object"