 # A problem with modulus and filter chaining

Tell us what’s happening:

Hi guys. So I already solved the challenge by having a look at the hints and figuring out I was only off by a bit. Thing is this: the code below solves all problems except for this:

squaredIntegers = squareList([-3.7, -5, 3, 10, 12.5, 7, -4.5, -17, 0.3])
// [9, 100, 49] expected output

My question is: why? I get that having two filter methods is stupid and I changed it after having a look at the solution. But I do not understand why n%parseInt(n) works for every case except this.

Okay nevermind, while writing this post I figured it out. parseInt(0.3) returns 0, therefore a 0.3%0 returns NaN because it results in a divide by zero.

I also noticed that I can not chain conditions in the following manner:
`.filter(n => n>0 && n%parseInt(n) ? null : n)`

This returns really weird values like this:
`[ 9, 23.04, 25, 9, 10.240000000000002 ] for the first array of [-3, 4.8, 5, 3, -3.2]`

Why does this conditional chain not work? does the use of the ternary operator void the “&&” ?
Okay holy duck, I think, again while writing, I figured it out. In this case the && does not mean “and” but it rather is the shorthand ternary that say “if the thing to the left is true, do the thing on the right” meaning if

n>0

is true it will do

n%parseInt(n

). But this in turn makes kinda little sense because thats the effect I want…kinda…no? I mean it is a filter function after all. This means it will execute the last statement in the chain, right? This means it will check n>0, and if thats true ( && ) it will try n%parseInt(n), if true return null, if false return the number n.
I can only guess that having a remainder of 0 does not result in a false?

I am sorry this got way more complicated than I anticipated. I hope I do not sound like a total idiot. My

``````
const squareList = (arr) => {
// only change code below this line
let newArr
newArr = arr
.filter(n => n%parseInt(n) ? null : n)
.filter(n=> n>0)
.map(n=> n*n)
console.log(newArr)
return arr;
// only change code above this line
};

const squaredIntegers = squareList([-3, 4.8, 5, 3, -3.2]);
console.log(squaredIntegers);

``````

User Agent is: `Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.87 Safari/537.36`.

Challenge: Use Higher-Order Functions map, filter, or reduce to Solve a Complex Problem

You would need to wrap ( and ) around the ternary expression. This does not help solve the problem as the ternary’s false value is number. Any number that is not zero is “truthy”.

``````  newArr = arr
.filter(n => n>0 && (n%parseInt(n) ? null : n))
.map(n=> n*n)
console.log(newArr)
``````

With the filter method you can not change the value of the array elements. Instead it only keeps or removes element based on the callback function returning true or false (respectively).

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