ES6

Question 1

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

Answer 1

A code block is code contained between a pair of curly braces. E.g. { const a = 5; console.log(a); }

Question 2

What does block scope mean?

Answer 2

A variable with block scope is accessible only within the code block it was declared in.

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

const variables cannot be reassigned, let variables can.

Question 5

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

Answer 5

Because the variable address is not being changed.

Question 6

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

Answer 6

Use const unless you need to reassign let.

Question 7

What is the syntax for writing a template literal?

Answer 7

Write string in between backticks like this

Question 8

What is “string interpolation”?

Answer 8

Substituting a piece of the string for results of expressions.

Question 9

What is destructuring, conceptually?

Answer 9

Taking the value of a property from an object and assigning it to a variable.

Question 10

What is the syntax for Object destructuring?

Answer 10

const { variable } = objectExample;

Question 11

What is the syntax for Array destructuring?

Answer 11

const [one, two, three] = [1, 2, 3];

Question 12

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

Answer 12

In destructuring, the brackets are on the left of the assignment operator, whereas when Object/Array literals are being created the brackets are on the right.

Question 13

What is the syntax for defining an arrow function?

Answer 13

parameter => code;
e.g. x => x + 2;
Add parentheses if more than one parameter and curly braces if more than one line of code.

Question 14

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

Answer 14

There can only be one expression and no statements.

Question 15

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

Answer 15

In an arrow function, this captures the this value of its enclosing context during definition instead of creating its own during call time.

Question 16

What are the three states a Promise can be in?

Answer 16

Pending, fulfilled, and rejected.

Question 17

How do you handle the fulfillment of a Promise?

Answer 17

.then(result => {})

Question 18

How do you handle the rejection of a Promise?

Answer 18

.catch(err => {})

Question 19

What is “syntactic sugar”?

Answer 19

Syntax within a language to make things easier to express and read.

Question 20

What is the typeof an ES6 class?

Answer 20

function

Question 21

Describe ES6 class syntax.

Answer 21

class {
constructor(params) { codeblock }
method() { codeblock }
}

Question 22

What is “refactoring”?

Answer 22

Restructuring existing code without changing its external behavior.

Question 23

How are ES Modules different from CommonJS modules?

Answer 23

ES Modules are imported statically and more often used for browsers where CommonJS modules are imported with functions and commonly used for Node.

Question 24

What kind of modules can Webpack support?

Answer 24

Both ES6 and CommonJS.