The sum of all integers between two numbers

Codewards Question

Given two integers a and b, which can be positive or negative, find the sum of all the numbers between including them too and return it. If the two numbers are equal return a or b.

NOTE: a and b are not ordered!

Examples

GetSum(1, 0) == 1 // 1 + 0 = 1
GetSum(1, 2) == 3 // 1 + 2 = 3
GetSum(0, 1) == 1 // 0 + 1 = 1
GetSum(1, 1) == 1 // 1 Since both are same
GetSum(-1, 0) == -1 // -1 + 0 = -1
GetSum(-1, 2) == 2 // -1 + 0 + 1 + 2 = 2

Solution 

function GetSum( a,b ) {
  let min = Math.min(a, b), max = Math.max(a, b);
  return (max - min + 1) * (min + max) / 2;
}

// TESTING
Test.describe("Basic Tests:", function(){

        Test.assertEquals(GetSum(0,-1),-1);
        Test.assertEquals(GetSum(0,1),1);
});