12 December, 2020
Guide Fari

TIL(Friday 12 Dec 2020)

Old code

{characters.map((character) => {

This didn't render the JSX elements

Fix from Andy

{characters.map((character) => {
	return (
		<h4 key={character.name}>{character.name}</h4>

This one is rendering and working just fine

another suggestion from Andy

{characters.map((character) => <h4 key={character.name}>{character.name}</h4>)}

This should also work

source for the next code blocks

const implicit = () => 'awesome'
implicit()    // returns 'awesome'

This also works if the function body is defined on multiple lines.

const implicit = () =>
implicit()    // returns 'awesome'

By this logic, using multiline return in my initial jsx code blocks, I can write that little block like this with no issue:

{characters.map((character) => 
	<h4 key={character.name}>

status - confirmed, it works. This multiline implicit return is also seen on some react documentation.

What I'm used to

{characters.map((character) => (
		<h4 key={character.name}>{character.name}</h4>

This one is also rendering and working just fine.

Return statement

When a return statement is used in a function body, the execution of the function is stopped. - source If the value is omitted, undefined is returned instead.

Interrupt a function

A function immediately stops at the point where return is called.


The map() function expects a callback as the argument and executes it once for each element in the array.

from the callback parameters, you can access:

  1. current element
  2. current index
  3. the array itself
const num = [3, 8, 11, 7, 5];

const num2x = num.map((n) => n * 2);

console.log(num2x); // [6, 16, 22, 14, 10]

Arrow function


(a, b) => a + b + 100; - displayed here is implicit return

if the body requires additional lines of processing, you'll need to re-introduce brackets PLUS the "return" (arrow functions do not magically guess what or when you want to "return"):

(a, b) => {
  let chuck = 42;
  return a + b + chuck;