How to group by an array of numbers?

JavaScript
1

I know how to do this in SQL lol, but not in JS.

If you have an array like this = var arrayRepeatedNumbers = [100,100, 20, 10,10,10]

How can you group them by amount?

Example:

var arrayNonRepeated = [Hundreds: 2, Twenties: 1, Tens: 3]

3 
(() => {

// add definitions in here.
const dictionary = new Map([
    [10, 'Tens'],
    [20, 'Twenties'],
    [100, 'Hundreds']
]);

// your test values
const arrayRepeatedNumbers = [
    100, 100, 20, 10, 10
];

// will hold a map of repeating values
const mapNonRepeated = new Map();

arrayRepeatedNumbers.forEach((number) => {

   // stores dictionary key
   const dictionaryKey = dictionary.get(number);
   
   // checks if key exists in your final map
   const keyExists = mapNonRepeated.has(dictionaryKey);

   // if key exists in map add one to it
   if (keyExists){
       let value = mapNonRepeated.get(dictionaryKey);
       mapNonRepeated.set(dictionaryKey, value = value + 1);
       return;
   }

   // otherwise set it to 1
   mapNonRepeated.set(dictionaryKey, 1);
});

console.log(mapNonRepeated);
//Map(3) {"Hundreds" => 2, "Twenties" => 1, "Tens" => 2}

// Map has some advantages over the standard Object.

})();
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