this doesn't pass all the time,

Why is the correct answer 1 in this test? because the element with index 2 is less than 'n'

Test.assertSimilar(howManySmaller([1.1888,1.1868,1.1838],1.19), 1);

Thanks! I will try another solution

Not with null, no.

as I understand it, in this example, you cannot use a loop for

Any line where you use length without properly checking if it is an array before.

tell me which line is the error. when you click on the test, the result is correct. attempt length error.

One of the tested inputs is null. Your function needs to be able to handle it, but as you have it written now, the function fails because you try to find the length of null.

how. in the loop we go through the array and the length is set there correctly, as I understand it. further, if the value is greater than the lesser and less than the greater, we add it to the variable sum. I don't understand where the error is, I'm a beginner developer.

Read the error message: TypeError: Cannot read property 'length' of null it's not the length what is null, it's the value passed to your function, and null has no length.