So calling two separate where-filters is a logical AND, while combining two where-filters in one where-call is an OR?

// SELECT studentName, teacherName FROM teachers, students WHERE teachers.teacherId = students.tutor AND tutor = 1
query().select(student).from(teachers, students).where(teacherJoin).where(tutor1).execute(); //[{"studentName":"Michael","teacherName":"Peter"}] <- AND filter
// SELECT * FROM number WHERE number < 3 OR number > 4
query().select().from(numbers).where(lessThan3, greaterThan4).execute(); //[1, 2, 5, 7] <- OR filter

The last test from Numbers tests. It uses two conditions in where statements as logical OR instead of logical AND.
Please update the description of the task accordingly.

A Functional Programming kata with array mutation!
That's weird.
Don't waste your time on it!

More better now ;-)

It can be dangerous in this case if, for example, you are executing this code on your server based on user input.

its only dangerous when missusing it :) often peapole dont even know that they us it, because its hidden in other functions ;)

This is not a JS problem. It is a floating point problem, it happens on other languages.

0.2 + 0.1 == 0.30000000000000004
It's a well known issue of JS itself

just a try, for 0.1+0.2=0.3
but it doesn't work

You should not be using eval, it is dangerous.

It's not perfect ;-)
Try that:

it("should sum only numbers and calculate the correct number", function(){
    Test.assertEquals(sum([5, '3', 2, '$', 1, NaN]), 8, "Sum equals to 8");
    Test.assertEquals(sum(['3', 0.2, '$', 0.1]), 0.3, "Sum equals to 0.3");
});