.forEach, .map, .filter, .reduce, .find

For the following lesson please review For Loops!

Why write for loops over and over? they involve way too much writing, they're prone to syntactical errors.

In the words of Jon Zachary:

Terser Syntax => less typos => happier developers => world peace

.forEach()

Call the forEach method on any array, pass it a callback function which invokes three agruments(Optional):

the element value
the element index
the array being traversed

const arr = ['a', 'b', 'c', 'd', 'e']

arr.forEach(function(el){
    console.log(el)
})

//expected output
=> 'a'
=> 'b'
=> 'c'
=> 'd'
=> 'e'

arr.forEach((d, i, a) => {
    console.log(`this is ${d}, this is the index ${i}, this is the array being traversed: ${a}`)
})

//expected output
=> "this is a, this is the index 0, this is the array being traversed: a,b,c,d,e"
=> "this is b, this is the index 1, this is the array being traversed: a,b,c,d,e"
=> "this is c, this is the index 2, this is the array being traversed: a,b,c,d,e"
=> "this is d, this is the index 3, this is the array being traversed: a,b,c,d,e"
=> "this is e, this is the index 4, this is the array being traversed: a,b,c,d,e"

##.map()

Use the .map() method on any array, it will return a new array with new mutated values.

let arr = [1, 2, 3, 4, 5]

const mapped = arr.map( d => d * 2 ); 

console.log(mapped)

//expected output:

=> [2, 4, 6, 8, 10]

.filter()

This method creates a new array with all the elements that pass the test implemented by the function... or it FILTERS everything you're not looking for.

let names = ["Carlos", "Dmitriy", "Angel", "Ester", "Alberto", "Magnardo"]

const filtered = names.filter( name => name.length > 5); 

console.log(filtered)

//expected output: 

["Carlos", "Dmitriy", "Alberto", "Magnardo"]

Use the .find() method on any array and it returns the value of the first element in the arrat that satisfies the callback function, otherwise undefined is returned. Just like the .forEach() method, the callback function also can take three arguments.

const arr = [5, 6, 30, 35, 90, 130,  9]; 

let found = arr.find((d) => {
    return d > 30; 
});

console.log(found); 

//expected output
=> 35

coderhero/forEach-map-filter-reduce-find

.forEach, .map, .filter, .reduce, .find

.forEach()

.filter()

.reduce()

.find()