为什么javascript返回-0

Question

I am trying to write a code that shows the last digit (in a set of 3) is the same. I could not understand why I got false for each set so, I decided to test -20%10 and I got -0 meanwhile 20%10 gives me the expected 0. What is this -0 about?

 function last_digit( x, y, z){ if(x % 10 == y % 10 == z % 10 ){ return true; }else { return false; } } console.log(last_digit(20, 30, 400)); console.log(last_digit(-20, 30, 400)); console.log(last_digit(20, -30, 400)); console.log(last_digit(20, 30, -400)); 

Answer 1

You need to compare the values pair wise with a logical AND && , because the first comparison returns a boolean value and the next is comparing this value with the rest of the following expression.

 function last_digit(x, y, z) { return x % 10 == y % 10 && x % 10 == z % 10; } console.log(last_digit(20, 30, 400)); console.log(last_digit(-20, 30, 400)); console.log(last_digit(20, -30, 400)); console.log(last_digit(20, 30, -400)); 

Answer 2

Do it this way,

 function last_digit(x, y, z) { if ((x % 10) == (y % 10) && (y % 10) == (z % 10)) { return true; } else { return false; } } console.log(last_digit(20, 30, 400)); console.log(last_digit(-20, 30, 400)); console.log(last_digit(20, -30, 400)); console.log(last_digit(20, 30, -400));