JS Arrays, Modern JavaScript & a little TypeScript Execute Program
How would you extract only the name of Betty's Car using destructuring? const user = { name: 'Betty', cat: { name: 'Keanu', age: 2, }, };
const {cat: {name}} = user;
Any value can be used as a ___________. For example, we can use an object as a default value.
default
Elements can be deleted from a set with the .___________ method. And the entire set can be cleared with .__________.
delete clear
Assignments with let, const, and the legacy var syntax can all use ________________________. (breaking apart arrays)
destructuring
The find method returns the ____________ itself
element
This code: const user = {name: 'Amir', age: 36} delete user would result in an __________
error
What would be the result of the following code? const user = { name of the user() { return 'Amir' } } user.name()
error
______________________ are never allowed in types (ex. 1 + 1 or true || false)
expressions
JavaScript classes can __________ (inherit from) other classes by declaring class MySubclass extends MySuperclass
extend
The some method always returns ________ for an empty array.
false
instantiate() instanceof Dog; returns ____________
false
what would this code return? class Cat { } true instanceof Cat;
false
Always user ________ after calling new Array(someSize). to avoid empty slots.
fill
The _________- method fills an array with a given value. Any existing values will be overwritten by that value.
fill
This is an example of a ______________ method because it defines a method inside of an object literal const user = { name() { return 'Amir'; } }; user.name();
shorthand
const user = { name() { return 'Amir'; } }; user.name(); The above code is an example of a _____________ method
shorthand
Skipping indexes like this is called "_____________ array destructuring".
sparse
Set is a built in JS class that we can use to more efficiently check if a collection includes a ___________- element.
specific
Methods defined on the classes themselves are called ______________________________
static methods
Order matters when setting object keys. When defining an object literal, the last value assigned to a key _______.
wins
Can you store 'surprise' elements on arrays in JavaScript?
yes
What does this code return? function returnsItsArguments(strings, ...values) { return { strings: strings, values: values, }; } returnsItsArguments`one${2}`;
{strings: ['one',''], values: [2]}
What keyword can we use when we want to assign a variable name that we don't want to change?
const
Does the forEach loop return hidden or surprise array properties?
no
SHOULD you store 'surprise' elements on arrays in JavaScript?
no
let sum: number = 1 + 1; sum; In the code above we are assigning the result sum to the type ___________
number
What does this code return? typeOf [];
object
What does this code return? typeOf {};
object
For for _____ loop loops over the values
of
The function remembers its ___________ name, even if it's assigned to a different variable.
original
The ____________ method turns a JSON string back into an object.
parse
Ultimately, the accessor is just another ____________ on the instance object.
property
The second argument in the JSON.stringify method is called the _________
replacer
The get and set keywords are ____________ when creating getters and setters.
required
const letters = ['a', 'b', 'c', 'd']; a) const [a, b, c] = letters; b) const a = letters[0], b = letters[1], c = letters[2]; A & B return the ___________ thing
same
Classes inside function have access to variables that are in ___________ within that function.
scope
In the following code, the toJSON key is telling the user object how it should be _________________- when the JSON.parse method is invoked on it. const user = { name: 'Amir', toJSON: () => 'This is Amir!' };
serialized
The server is whatever ___________ the data to the client.
serves
Methods defined inside of an object literal are called "______________- methods".
shorthand
True or False? Return is implicit in Javascript.
False
The _________ keyword doesn't stop us from mutating (changing) the value held by the variable. For example, we can mutate a const array by calling its push method.
const
( () => 1 ).name;
''
What is the result of this code? JSON.stringify([1, undefined, 2]);
'[1,null,2]'
function five() { return 5; } five.name; What is returned here?
'five'
const one = () => 1; one.name;
'one'
What does this code return? const abc = [true, true, true]; abc.indexOf(false);
-1
What is the result of this code? let sum: number = 1 + 1; sum;
2
const arr = ['a', 'b', 'c']; arr.six = 6; arr['six']; What does the last line return?
6
Does JS throw an error when you forget to include an argument for a parameter?
No
_____________-It is the intentional absence of the value. It is one of the primitive values of JavaScript
Null
The original isNaN function was a mistake, and _____________________ should be preferred in all circumstances.
Number.isNaN
_____ contain only unique values. If we .add a value that already exists in the set, nothing happens; the set is unchanged.
Sets
____________- with objects means "include all of that object's properties in this object".
Spreading
Is this TypeScript only or Javascript only? type MyNumberType = number;
TypeScript
_______________It means the value does not exist in the compiler. It is the global object.
Undefined
What are the keys for this array in JS? Object.keys(['a','b','c'])
['0','1','2']
What will this code return? const arr1 = ['a', 'b']; arr1.five = 5; Object.keys(arr1);
['0','1','five']
What will this code return? const letters = ['a', 'b', 'c']; const [a, b, c, d='dee', e] = letters; [d, e];
['dee', undefined]
Classes can be ______________ (have no name), and they can be _____________ (the class definition itself is used as an expression).
anonymous inline
When defining a function with an explicit function type, we can only use the newer ______ _______________syntax:
arrow function
If the template literal ends in an interpolated value, like `age: ${age}`, JavaScript will insert one more empty string, '', _________________-
at the end
Interpolate in JavaScript with ______________
backticks
JSON can't represent ___________ objects.
circular
Inside of a static method or accessor, this refers to the _________ itself.
class
The _______________ can be a browser, an iOS device, etc.
client
The compiler forces us to use types correctly. If we use them incorrectly, it's a type error and the program won't ___________.
compile
.flat(Infinity) this flattens the array ___________
completely
We use [square brackets] when we want a ______________ property name. Ex. const key = 'name'; const {[key]: value} = {name: 'Amir'}; value;
computed
If we immediately assign an anonymous function to a variable, that variable's name will become the _______________ name. (Functions created like this are still called "anonymous")
function's
Internally, JavaScript classes are just ______________.
functions
With hooks, the classes disappear and we just write ___________.
functions
The for _____ loop loops over the indices
in
When TypeScript determines the type for us without us explicitly writing it We call this type _______________, and we say that TypeScript infers types.
inference
We can't define a class ___________ another class. That causes an error, whether we use the class or not.
inside
A circular object is an object that references ___________
itself
To the object, the function name is just another _________!
key
The for in loop returns _________
keys
push returns the array's ____________, including the newly-pushed element.
length
With the keyword _______, a variable defined inside the if isn't visible outside the if
let
we recommend that you always use _________ instead of var when declaring variables
let
The important thing to know is that the replacer function exists, and that the replacer gets a chance to ____________ every part of the object as it's stringified.
modify
What is the "hidden" property of this function that we can call? function five() { return 5; } five.________; (it will return 'five')
name
If you want to use punctuation you must use ____________________________
string keyed methods
const user = { 'name of the ~user~'() { return 'Betty'; } }; user['name of the ~user~'](); In the above code this method definition syntax is called __________- __________- __________ because we're using the normal JavaScript string syntax to define the method's name
string keyed methods
The ___________ method turns a JavaScript object or value into a JSON string. By default, it will pack the JSON tightly
stringify
sort converts the array's elements to ___________--, then compares them. Because it compares strings, it inherits the comparison problem above.
strings
If the subclass has a constructor, it has to call _____________() in its constructor before accessing any this properties.
super
'3' > '10'
true
True or false? In JavaScript, there is no syntax for multiple inheritance.
true
true or false? Anonymous functions only get a name if they're assigned directly to a variable
true
In JavaScript, any code with valid syntax will run. In TypeScript, code must have valid syntax and must ______________________. Only then will it run.
type check
When the compiler accepts a program's types, we say that that program ______________________-.
type checks
_________________ is when the types are used for type checking, then erased from the compiled output.
type erasure
What is a nifty JSON method to type check something?
typeof
The special case dealing with stringify and parse is ______________
undefined
When we call a JavaScript function with an argument missing, the corresponding parameter gets the value _______________.
undefined
const obj = {}; obj.defaultName; returns ____________
undefined
At each step, our replacer function can do three things: Return the value argument _______________, which won't change the stringified object. Return some _________ value, which will replace the original value in the stringified JSON. Return ____________-, which will remove the key from the stringified JSON.
unmodified other undefined
The short version is: const applies to the variable, not the __________ held by the variable.
value
the For of loop returns _____________
values