ES6

Question 1

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

Answer 1

Blocks are notated by curly braces, loops often times

Question 2

What does block scope mean?

Answer 2

Means that the variable within the block will not be accessible from outside the block.

Question 3

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

Answer 3

Block scope

Question 4

What is the difference between let and const?

Answer 4

let ‘s value can be reassigned const can not.

Question 5

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

Answer 5

Because we can change the arrays elements but we cannot reassign the const variable to a new array.

Question 6

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

Answer 6

if the value needs to be reassigned, use let, otherwise use const.

Question 7

What is the syntax for writing a template literal?

Answer 7

` text ${expression}`

Question 8

What is “string interpolation”?

Answer 8

the JavaScript engine will automatically replace these variables ${} and expressions with their values

Question 9

What is destructuring, conceptually?

Answer 9

were taking properties or array element values, extracting them to their own variables.

Question 10

What is the syntax for Object destructuring?

Answer 10

let {propKey1: propAlias1, lastname} = object.

Question 11

What is the syntax for Array destructuring?

Answer 11

let [x,y,z] = array

Question 12

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

Answer 12

the curly brackets are on the left side of the assignment operator.

Question 13

What is the syntax for defining an arrow function?

Answer 13

(param1, param2) => {
return;
}

param => exp;

() => exp;

Question 14

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

Answer 14

evaluated as an expression not a statement. result of that expression is returned, implicit return.

Question 15

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

Answer 15

lexically, it takes the this from the enclosing function. it is determined at definition for arrow functions. call time for es5 functions.

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.

state cannot be changed

Question 17

How do you handle the fulfillment of a Promise?

How do you handle the rejection of a Promise?

Answer 17

The then() method returns a Promise. It takes up to two arguments: callback functions for the success and failure cases of the Promise.

Question 18

How do you handle the fulfillment of a Promise?

Answer 18

The catch() method returns a Promise and deals with rejected cases only. you pass it a callback function

Question 19

What is “syntactic sugar”?

Answer 19

syntactic sugar is syntax within a programming language that is designed to make things easier to read or to express.

Question 20

What is the typeof an ES6 class?

Answer 20

a function

Question 21

Describe ES6 class syntax.

Answer 21

class Person {
   optional constructor(name) {
        this.name = name;
    }
    getName() {
        return this.name;
    }
}

Question 22

What is “refactoring”?

Answer 22

code refactoring is the process of restructuring existing computer code—changing the factoring—without changing its external behavior. Refactoring is intended to improve the design, structure, and/or implementation of the software (its non-functional attributes), while preserving its functionality

Question 23

How are ES Modules different from CommonJS modules?

Answer 23

ES modules are the standard for JavaScript, while CommonJS is the default in Node. js.
the way you import and export them.

import keyword

export default class name

Question 24

What kind of modules can Webpack support?

Answer 24

ECMAScript modules. CommonJS modules. AMD modules.