ES6 (JavaScript)

Question 1

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

Answer 1

A group statements between curly braces.

i.e., a function code block or a if statement code block.

Question 2

What does block scope mean?

Answer 2

Block scope restricts the access to a variable to only within its code block.

Question 3

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

Answer 3

Blocked scope.

Question 4

What is the difference between let and const?

Answer 4

Variables declared using let are mutable (can be reassigned).

Variables declared using const are immutable (cannot 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 const keyword creates a variable that is read-only.

The array assigned to a const variable can be modified, but the const variable itself cannot be assigned a new array or other value.

Question 6

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

Answer 6

Whether the developer intends to reassign a variable.

Question 7

What is the syntax for writing a template literal?

Answer 7

A string or (optional) JavaScript expressions in between backticks.

Question 8

What is “string interpolation”?

Answer 8

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

Question 9

What is destructuring, conceptually?

Answer 9

A (alternative) way to assign properties of an object to variables or assign elements of an array to variables.

Question 10

What is the syntax for Object destructuring?

Answer 10

The const keyword followed by curly braces. Inside the curly braces is the property of an object and variable name separated by a colon. After the curly brace is an assignment operator followed by the name of the object and semicolon.

Question 11

What is the syntax for Array destructuring?

Answer 11

The const keyword followed by square brackets. Inside the square brackets are variable names separated by commas. After the square brackets is an assignment operator followed by the name of the array and semicolon.

Question 12

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

Answer 12

Objects use curly braces and arrays use square brackets.

Question 13

What is the syntax for defining an arrow function?

Answer 13

Parameters separated by commas inside parenthesis (if any/two or more) followed by an arrow. After the arrow, there can either be an expression or an arrow function body that has a return operator then a semicolon.

Question 14

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

Answer 14

Without curly braces, the arrow function returns the result of an expression (implicit return expression) instead of returning a value.

Question 15

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

Answer 15

The value of this determined by it’s surrounding code block.

The value of this is determined when the arrow function is defined.

Question 16

What are the three states a Promise can be in?

Answer 16

Pending: Initial state, neither fulfilled nor rejected.

Fulfilled: The operation was completed successfully.

Rejected: The operation failed.

Question 17

How do you handle the fulfillment of a Promise?

Answer 17

By calling the .then() method on the promise object.

Question 18

How do you handle the rejection of a Promise?

Answer 18

By calling the .catch() method of the promise object.

Question 19

What is “syntactic sugar”?

Answer 19

Code syntax that is written in a way that is easy to read or express clearly.

Question 20

What is the typeof an ES6 class?

Answer 20

The ‘function’ data type.

Question 21

Describe ES6 class syntax.

Answer 21

The class keyword followed by the name of the class (capitalized) and the code block.

Within the code block, there is a constructor definition and optional method definitions separated by a line space.

Question 22

What is “refactoring”?

Answer 22

The process of improving the design or implementation of existing code while preserving functionality.

Question 23

How are ES Modules different from CommonJS modules?

Answer 23

ES Modules (Official)
- Files are imported using the ‘import’ statement.
- Files are exported using the ‘export’ statement.

CommonJS Modules (Community)
- Files are imported using ‘require’ function.
- Files are exported using the ‘exports’ property.

Question 24

What kind of modules can Webpack support?

Answer 24

Both ES and CommonJS modules are supported.

Question 25

What does fetch() return?

Answer 25

A promise that resolves to a response object.

Question 26

What is the default request method used by fetch()?

Answer 26

The GET request method.

Question 27

How do you specify the request method (GET, POST, etc.) when calling fetch?

Answer 27

By setting the method property to the desired request method in the options parameter of the fetch method call.