ES6 JS

Question 1

When an arrow function’s body is left without curly braces, what changes in its functionality?

Answer 1

without {} the result will be auto returned

with {} you have to add return mannuly

Question 2

How is the value of this determined within an arrow function?

Answer 2

when the function defined

Question 3

How is the value of this determined within a normal function?

Answer 3

call time

Question 4

What is destructuring, conceptually?

Answer 4

Destructuring is a convenient way of extracting multiple values from data stored in (possibly nested) objects and Arrays.

Question 5

What is a code block? What are some examples of a code block?

Answer 5

Function in if, for, while loop (code with {})

Question 6

What does block scope mean?

Answer 6

the variable outside the block can be use in block, but the variable in block cannot be use in outside

Question 7

What is the scope of a variable declared with const or let?

Answer 7

they can’t scope to outside

Question 8

What is the difference between let and const?

Answer 8

const cannot change (ex: minute per hour, book name…)

let can be change

Question 9

Why is it possible to .push() a new value into a const variable that points to an Array?

Answer 9

because it’s change the property of object, not abject

Question 10

How should you decide on which type of declaration to use?

Answer 10

use let when the value probably change in the futures , const for the value that gonna always be the same

Question 11

What is the syntax for writing a template literal?

Answer 11

xxxx

Question 12

What is “string interpolation”?

Answer 12

a string contains varible and algorithms.
xxxx${xx}xx

Question 13

What is the syntax for Object destructuring?

Answer 13

const { title, author, libraryID } = book1;
const { title: title2, author: author2, libraryID: libraryID2 } = book2;

Question 14

What is the syntax for Array destructuring?

Answer 14

const [book3, book4, book5] = library;

Question 15

How can you tell the difference between destructuring and creating Object/Array literals?

Answer 15

object is {} array is []

Question 16

What is the syntax for defining an arrow function?

Answer 16

xxx = (parameters1, parameters2) => xxx
if only one expression, {} is not need.
multiple lines expression needs be surround by {}

Question 17

How do you handle the fulfillment of a Promise?

Answer 17

promise.then()

Question 18

How do you handle the rejection of a Promise?

Answer 18

promise.catch()

Question 19

error

Answer 19

error is object, has message and other key>
console.log() call the
console.dir() call the
console.error() make it to red error

Question 20

reduce(accumulator, currentValue)

Answer 20

can make accumulator an Array of functions to process currentValue multiple times by the reduce function