createDictionary.ts

createDictionary.ts

const getCounts = <T,>(
    input: Iterable<T>,
    shouldCountCb: (input: T) => unknown,
    serializeKey: (input: T) => any = input => input,
) => {
     let counts = {} as Record<any, number>
     for(let val of input){
        if(shouldCountCb(val)){
         counts[serializeKey(val)] = (counts[serializeKey(val)] ?? 0) + 1
        }
     }
     return counts
}

const isVowel = (
    input: string, includeY: boolean  = false
)  => [...["a", "e", "i", "o", "u"], ...(includeY ? ["y"] : [])]
      .includes(input.toLowerCase())



console.log(getCounts("hello", isVowel ))
console.log(getCounts(["h", "e", "l", "l", "o", ], isVowel))

const people = [
    {name: 'jon', age: 10},
    {name: 'jonn', age: 20},
    {name: 'jonnn', age: 21},
    {name: 'jonnnn', age: 20},
    {name: 'jonnnnn', age: 21},
    {name: 'jonnnnn', age: 23},
    {name: 'jonnnnnnn', age: 32},
    {name: 'jon', age: 10},
]

const peopleBetween20And30Counts = getCounts(
    people,
    person => person.age >= 20 && person.age <= 30,
    person => person.age,
)

console.log(peopleBetween20And30Counts)