ES6

Question 1

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

Answer 1

the opening and closing of curly braces { } (denoted by curly braces). for, if, while are examples of code block.

Question 2

What does block scope mean?

Answer 2

the variable defined within a block (code block) will not be accessible from outside the block (code block)

Question 3

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

Answer 3

they are blocked-scope. while var function-scope.

Question 4

What is the difference between let and const?

Answer 4

variable declared with a const won’t be reassigned read-only reference. variable declared with a let may be reassigned, mutable (such as a counter in a loop, or a value swap in an algorithm.)

Question 5

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

Answer 5

method .push() does not reassign the array. in const adding/removing elements is allowed since it’s not a reassignment. push() is mutation same as pop etc.

Question 6

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

Answer 6

use let if the variable is reassigned at any time of the code, else use const if not being reassigned.

Question 7

What is the syntax for writing a template literal?

Answer 7

by wrapping text in backticks ( string string ${'yoon'.toUpperCase()} )

Question 8

What is “string interpolation”?

Answer 8

the ability to substitute part of the string for the values of variables or expressions.

Question 9

What is destructuring, conceptually?

Answer 9

extracting elements from arrays or properties from objects, and assigning them to different variables.

Question 10

What is the syntax for Object destructuring?

Answer 10

const { property: theNewVariable, property: theNewVariable, propKey(if want same variable) } = object

Question 11

What is the syntax for Array destructuring?

Answer 11

const [ variable, variable] = array;

Question 12

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

Answer 12

It is located on the left side of the assignment operator

when creating a object/array literals, a variable name is followed by the var, let, const keyword. however in destructuring, object literal or array literal is followed by those keywords.

Question 13

What is the syntax for defining an arrow function?

Answer 13

var, let, const(keyword) variable = (param(s)) => { statements }

(param1, param2) => {
return;
};

param => expression;

() => expression;

Question 14

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

Answer 14

without the curly braces { } the arrow function has an implicit return. evaluated as an expression and returned.

Question 15

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

Question 16

What are the three states a Promise can be in?

Answer 16

pending: initial state, neither fulfilled nor rejected
fulfilled: meaning that the operation was completed successfully
rejected: meaning that the operation failed

can only go from pending to resolved OR pending to rejected

Question 17

How do you handle the fulfillment of a Promise?

Answer 17

use the then() method, it returns a promise.
Promise.then( (value) => {
console.log(value);
});

pass in a callback function in the then(callback);

Question 18

How do you handle the rejection of a Promise?

Answer 18

the catch() method, it returns a promise and deals with rejected cases only.

Promise.catch( (error) => {
console.error( error.message );
});
look up Error.prototype.message on MDN, message property is a human-readable description of the error.

Question 19

What is Array.prototype.filter useful for?

Answer 19

it filters down to just the elements from the given array that pass the test implemented by the provided function

Question 20

What is Array.prototype.map useful for?

Answer 20

creates a new array populated with the results of calling a provided function on every element in the calling array

Question 21

What is Array.prototype.reduce useful for?

Answer 21

is to return the sum of all the elements in an array,

Question 22

What is “syntactic sugar”?

Answer 22

is syntax within a programming language that is designed to make things easier to read or express or write. makes the language sweeter for human use: expressed more clearly, concisely, in alternative style that some may prefer.

Question 23

What is the typeof an ES6 class?

Answer 23

function

Question 24

Describe ES6 class syntax.

Answer 24

class ClassName {
    (optional) constructor(param, param2) {
        this.param = param;
        this.param2 = param2;
    }

getMethod() {
    return this.method() ex this.name
} }

Question 25

What is “refactoring”?

Answer 25

is the process of restructuring existing code, chaging the factoring, without changing its external behavior. is intended to improve the design, structure, and/or implementation of the software while preserving its functionality. code does the exact same thing, but easier to read/understand, also easier to make changes to as the code grows

Question 26

How are ES Modules different from CommonJS modules?

Answer 26

commonJS = provides modules

ES Modules = dedicated keyword for import and export

Question 27

What kind of modules can Webpack support?

Answer 27

CommonJS Modules, AMD modules, and ECMAScript Modules