Glossary

Question 1

When is code Asynchronous?

Answer 1

Code is asynchronous when you initiate something, forget about it, and when the result is ready you get it back without having to wait for it. It might take even seconds and in the meantime you complete other stuff, and when the response it ready, the callback function gets called.

Question 2

What’s an example of Asynchronous?

Answer 2

AJAX call.

Question 3

What’s a modern way to handle async?

Answer 3

Promises and async

Question 4

In JavaScript, Block is created by?

Answer 4

curly braces {}.

eg.) if statement contains a block, a for loop contains a block.

Question 5

Block Scoping

Answer 5

When a variable in a block is visible and accessible from inside the whole block, but not outside of it.

Question 6

Callback

Answer 6

A callback is function that’s invoked when something happens.

eg.) A click event associated to an element has a callback function that’s invoked when the user clicks the element. A fetch request has a callback that’s called when the resource is downloaded.

Question 7

Declarative

Answer 7

A declarative approach is when you tell the machine what you need to do, and you let if figure out the details.

Question 8

Why is React considered declarative?

Answer 8

Because you reason about abstractions rather than editing the DOM directly.

Question 9

A “Fallback” is used for?

Answer 9

Is used to provide a good experience when a user hasn’t access to a particular functionality.
eg.) a user that browses with JavaScript disabled should be able to have a fallback to a plain HTML version of the page. Or for a browser that has not implemented an API, you should have a fallback to avoid completely breaking the experience of the user.

Question 10

Function Scoping

Answer 10

Any variable defined in a function is visible and accessible from inside the whole function.

Question 11

Immutability

Answer 11

A variable is immutable when its value cannot change after it’s created.

Question 12

Mutable

Answer 12

A variable that can be changed.

Question 13

Lexical Scoping

Answer 13

A particular kind of scoping where variables of a parent function are made available to inner functions as well.

Question 14

Polyfill

Answer 14

A way to provide new functionality available in modern JavaScript or a modern browser API to older browsers.

Question 15

Pure Function

Answer 15

A function that has no side effects (does not modify external resources), and its output is only determined by the arguments. You could call this function 1M times, and given the same set of arguments, the output will always be the same.

Question 16

Reassignment

Answer 16

JavaScript with var and let declaration allows you to reassign a variable indefinitely. With constdeclarations you effectively declare an immutable value for strings, integers, booleans, and an object that cannot be reassigned (but you can still modify it through its methods).

Question 17

Scope

Answer 17

Scope is the set of variables that’s visible to a part of the program.

Question 18

Scoping

Answer 18

Scoping is the set of rules that’s defined in a programming language to determine the value of a variable.

Question 19

Shim

Answer 19

A shim is a little wrapper around a functionality, or API. It’s generally used to abstract something, pre-fill parameters or add a polyfill for browsers that do not support some functionality. You can consider it like a compatibility layer.

Question 20

Side effect

Answer 20

A side effect is when a function interacts with some other function or object outside it. Interaction with the network or the file system, or with the UI, are all side effects.

Question 21

State

Answer 21

State usually comes into play when talking about Components. A component can be stateful if it manages its own data, or stateless if it doesn’t.

Question 22

Stateful

Answer 22

A stateful component, function or class manages its own state (data). It could store an array, a counter or anything else.

Question 23

Stateless

Answer 23

A stateless component, function or class is also called dumb because it’s incapable of having its own data to make decisions, so its output or presentation is entirely based on its arguments. This implies that pure functions are stateless.

Question 24

Strict mode

Answer 24

Strict mode is an ECMAScript 5.1 new feature, which causes the JavaScript runtime to catch more errors, but it helps you improve the JavaScript code by denying undeclared variables and other things that might cause overlooked issues like duplicated object properties and other subtle things. Hint: use it. The alternative is “sloppy mode” which is not a good thing even looking at the name we gave it.

Question 25

Tree Shaking

Answer 25

Tree shaking means removing “dead code” from the bundle you ship to your users. If you add some code that you never use in your import statements, that’s not going to be sent to the users of your app, to reduce file size and loading time.