Help please

Question

Can someone help me with this...?

nums.filter(n => n % 2 == 0).map(el => sum+= el);

I don't understand, I'm in JS' rest parameter lesson, but there does not explain what in this line are

Answer 1

Look, i m gonna tell using simple function syntax, not arrow functions, to make things clear.

Here's an array
let array = [ 1, 2, 3, 4, 5 ]

Now I just wanna get an array with numbers ABOVE 2, so i would filter this array.

array.filter()

Now this filter takes something between those brackets, that something means "parameter" it takes a function as a parameter.

array.filter(function() { })

Now i wanna give a name so that i can refer to each single number inside of this array, i will just call it "number"

array.filter(function(number) { } )
Now inside the curly brackets, i will RETURN the numbers that are above 2, so,

array.filter(function(number) {
return number > 2
})

You can store the result inside a variable

Now that u know filter(), map() doesnt filter an array it just simply goes through an array and returns a new array, such as if u want to double each element inside an array

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

let doubledArray = array.map( function (num) {
return num * 2
})

// [2,4,6,8,10]

Answer 2

Bryan Martinez it literally made me smile :D im glad i could help

Answer 3

This is all the code

function magic(...nums) {
let sum = 0;
nums.filter(n => n % 2 == 0).map(el => sum+= el);
return sum;
}
console.log(magic(1, 2, 3, 4, 5, 6));

Answer 4

... parameter packs the arguments into an array
and nums.filter(n=>n%2==0).map(el=>sum+=el) is chaining of different methods so now filter returns an array which contains the elements whose remainder was 0 and then those elements are added together using map

Answer 5

@maf
seriously thank you very much, you born to teach, 'cause now I already understand each character, thanks.