the result must be a number. Perhaps you are returning a value to a function as a string. sorry for my english

There is no need to use conditional statement?
like this return code, if it gives boolean itself, doesn't need to use conditional statement, right?

ah ha Thanks !

I meant, arrow function doesn't need return. Read this: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions

but this solution didn't use 'return'

No.

does arrow function no need 'return'?

thanks!

const flip = (d, a) => {...}

is the same as:

function flip(d, a) {...}

d and a are arguments.

what is the meaning of (d, a) ?
I don't usually use arrow function

it's you

The important thing is to return a number type..! thank you I should try again

the method is not in first question here, instead compare the difference of data type used for the return: [] is an array type, and 0 is a number. (the function should return a number)

I use Bubble sort by using nested for loop and this loop need the [].
using Bubble sort is not that answer wants?

it means you returned [] but the test expected the result 0