Modern JS - Crash Course

Question 1

What is ECMAScript?

Answer 1

It is the specification that javascript conforms to.

Question 2

What is the name of the committee that maintains javascript?

Answer 2

Ecma TC39

technical committee 39

Question 3

How often TC39 releases new versions?

Answer 3

Yearly

Question 4

What is a block scope? Can they be nested?

Answer 4

It is curly braces {}, yes can be nested.

Question 5

Can we change the content of a const variable of a non scalar variable (primitive)

Answer 5

Yes. You just can’t change the reference to the object!

Question 6

What is the main difference of a regular js function and an arrow function?

Answer 6

The scope of this of the first will be the caller’s environment and the second will be the defining environment. Therefore, the this keyword of an arrow function depends WHERE it is called.

Question 7

What is a dinamyc property of an object literal? How is it declared?

Answer 7

It means the property will update another variable based on its content.

declared as
const myValue = 'answer'
const obj = {
  [myValue]: 42
}
obj.answer //42

Question 8

What is destructuring and how is it declared? Where is it used in React?

Answer 8

Destructuring means assigning references from a collection into separate variables.

declared as:
const {PI, E, SQRT2} = Math

Used in Hooks

Question 9

What does the … do in js?

Answer 9

They make a copy of something

Question 10

What is a template string?

Answer 10

It is a string that supports interpolation… e.g: hello ${user}

Question 11

What is a promise?

Answer 11

Is an object that may deliver data at a later time in the program

Question 12

How to consume a promise? What’s necessary after?

Answer 12

With “then”, where you need to supply a callback function.

Question 13

What is a modern way to fetch data without using promise-chain?

Answer 13

By using async and await. Instead of nesting “then” you can await each call.

Question 14

Is that possible to define css styles directly in the JSX? If so, how?

Answer 14

Yes, only use the styles={{margin: ‘20px’}}

Question 15

What is the best applicability of JSX styles? Does it replace regular css files?

Answer 15

For conditional styles. For other use regular CSS file instead.

Question 16

What is the createRef method? What is a better way of doing it?

Answer 16

Is a method that references the value from a html component into a field. A better way of doing it is via value and onchange methods

Question 17

How to fetch data from api? What is a better option?

Answer 17

using fetch… better use axios

Question 18

What happens when you are rendering a list of components without specifying a key element?

Answer 18

React will give a warning and it is necessary to define an unique id to each card.