You can use this method:

/*
  commented line
  commented line
*/

Or you can also use // on multiple lines:

// commented line
// commented line

if (number % 2 === 0) {
  // even
} else {
  // odd
}

Here are two functions you can use to determine if a number is even or odd:

const isEven = num => num % 2 == 0
const isOdd = num => num % 2 == 1

isEven(2) // returns true
isOdd(5)  // returns true

You can use those methods in your if...else statement.

You can create a custom string method like this:

String.prototype.yourMethodName = function() {
  return this // string is accessed via this
}

function uppercaseFirstLetter(string) {
  return string.charAt(0).toUpperCase() + string.slice(1)
}

string.charAt(0).toUpperCase() takes the first letter from the given string parameter and converts it to upper case. Then, string.slice(1) adds the rest of the string on to it.

Here's how you'd use it:

uppercaseFirstLetter("tacos") // returns "Tacos"