Just a great list of solutions that I wish I had thought of.

codeWarsSolutions

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



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

**********************************************************************
REALLY COOL WAY TO AVOID IF ELSE (BUT NOT IF ELSE IF...)

// JS Nuggets: Ternary Operator LINK: https://www.youtube.com/watch?v=s4sB1hm73tw

// condition ? expr1 : expr2

var age = 15;

if (age >= 18) {
	console.log("You are an adult!");
} else {
	console.log("You are a kid");
};

console.log((age >= 18) ? "You are an adult!" : "You are a kid.");

var stop;

age > 18 ? (
    console.log("OK, you can go."),
    stop = false
) : (
    console.log("Sorry, you are much too young!"),
    stop = true
);

var firstCheck = false,
    secondCheck = false,
    access = firstCheck ? "Access denied" : secondCheck ? "Access denied" : "Access granted";

console.log(access);