es6

Question 1

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

Answer 1

A block of code within the curly braces. Function, while, for, if else.

Question 2

What does block scope mean?

Answer 2

An area within the block where variables can be referenced.

Variables are only accessible within the block.

Question 3

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

Answer 3

let = block-scoped (within any code block { }. Ex. if (xx) {} for(xx) {})
const = block-scoped
var = function-scoped - if there is no function it is defined in, it’s globally scoped.

Question 4

What is the difference between let and const?

Answer 4

Const can’t be reassigned. The values of whatever it is assigned to can be manipulated or changed but you cannot reassign it.

Let can be reassigned.

Question 5

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

Answer 5

The value with the array is mutable.

Question 6

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

Answer 6

If the variable is not going to be reassigned, use ‘const’.
If the variable will be reassigned then use ‘let’.

Question 7

What is the syntax for writing a template literal?

Answer 7

Template literals use backticks rather than single or double quotes and commonly use string interpolation for JavaScript expressions or variables: ${variable} ${1 + 1}

Question 8

What is string interpolation?

Answer 8

A process where variables and expressions are embedded in a string. The variable/expression must be placed in a space block as follows: ${variable_name}

Question 9

What is destructuring conceptually?

Answer 9

Taking the values within an object or an array and assigning them to a variable.

Question 10

What is the syntax for object destructuring?

Answer 10

let { property1:variable1, property2: variable2} = object

Question 11

What is the syntax for array destructuring?

Answer 11

let [index1, index2] = array

Question 12

How can you tell the difference between destructuring and creating object/array literals?

Answer 12

Destructuring: the variable name goes on the right of the assign operator.
let/const {} or [] = variable name
Creating: variable name goes on the left of the assign operator
variable = {} or []

Question 13

What is the syntax for defining an arrow function?

Answer 13

(parameters separated by commas) => {}

If there is only 1 parameter the parentheses are not needed. If the return is a simple expression, brackets and return keyword can be omitted. Brackets and return keyword are needed for code block if it’s multiline statements.

Question 14

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

Answer 14

It becomes a return

Question 15

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

Answer 15

Arrow functions: the value of this is determined at definition time.
Regular functions: the value of this is determined at call time.

Question 16

What are the three states a promise can be in?

Answer 16

Pending: intitial state, neither fulfilled nor rejected.
Fulfilled: The operation was completed successfully.
Rejected: Meaning that the operation failed.

Question 17

How do you handle the fulfillment of a promise?

Answer 17

Use .then() method.

Question 18

How do you hand the rejection of a promise?

Answer 18

Use .catch() method.

Question 19

What is “syntactic sugar”?

Answer 19

designed to make things easier to read or to express. It makes the language “sweeter” for human use: things can be expressed more clearly, more concisely, or in an alternative style that some may lrefer.

Question 20

What is “refactoring”?

Answer 20

The process of restructuring existing code without changing its external behavior. Refactoring is intended to improve the design, structure and implementation of the software.

Question 21

How are ES6 modules different from commonJS modules?

Answer 21

CommonJS uses require() method to import and module.export to export.

ES6 modules use import and export statements.

Question 22

What kind of modules can Webpack support?

Answer 22

ECMAScript modules, CommonJS modules, AMD modules.

Question 23

What is temporal dead zone? (TDZ)

Answer 23

When you try to use a variable before its declared.

Question 24

Function declarations are hoisted to the top of script so you can call functions before where they’re defined.