How do I filter the unique values of a list using only integers or lists and without using any functions in JavaScript?

Question

I need to identify the unique values and put it to another list so that there are no repeated values in the other list. I cannot use functions like .filter() or .includes() or .push() anything like that because I am doing this on Code.org which is what my school uses and they restrict a lot of functions that I normally use.

I've tried:

function contains(city) {
  appendItem(filteredLocations, locations[0]);
 for (var i = 0; i <locations.length; i++);
  if (filteredLocations[i] != city){
    appendItem(filteredLocations, locations[i]);
  }
  else {
    i++;
  }
}`

and this:

function fillDropdowns(){ 
 //filter the cities
 for (var i = 0; i < locations.length;i++){
   if (contains(locations[i]) == true) {
     appendItem(filteredLocations, locations[i]);
   }
   else {
     i++;
   }
 }
 //locations list
 
}
function contains(city) {
 for (var i = 0; i < filteredLocations.length; i++);
  if (filteredLocations[i] == city){
    return true;
  }
}

And some others that I have deleted.

Answer 1

You just need to implement a js lookup object to check whether a key is unique or not.

const locations = ["Munich", "Frankfurt", "Nuremberg", "Munich", "Frankfurt"];

const dict = {}; //Look up object 
const uniqueCities = [];

for (let i = 0, j = 0; i < locations.length; ++i) {
  const city = locations[i];
  if (!dict[city]) { //if city is not in "dict" that means it's an unque city
    dict[city] = true; //pushing the unique city to "dict" because it's not unique anymore
    uniqueCities[j++] = city;
  }
}

console.log(uniqueCities);