Finds multiples of 3 and 5, then adds them together.

Multiples-of-3-and-5.js

//Create variable to hold sum.
var num = 0;

//For loop to iterate through 1000.
for (var i = 0; i < 1000; i++){
  
  //Find multiples of 3 and 5.
  if (i % 3 === 0 || i % 5 === 0){
    
    //Add them to num.
    num += i;
  }
}

console.log(num);