Identify duplicate elements in an array.

This function takes an array of numbers to create a new Set object. If an element is a duplicate, it will not be included in the Set object and will return?false. This value is then negated to?true, which allows the element to be added to the result array, which is ultimately returned.

The?.filter?method iterates over each array element, executing a provided callback function. This function determines whether an element should be included in the resultant filtered array. If the callback function returns?true?for an element, that element is included in the new array. The callback function, defining the filtering criteria, takes two arguments:?element?(the current element being processed), and?index?(the index of the current element in the array). If not needed, the?index?argument can be omitted. Importantly,?.filter?does not modify the original array, but creates a new one with the filtered elements.

A Set stores?unique values?and does not allow duplicate entries. It can contain elements of any data type, including numbers, strings, and objects. Sets maintain the insertion order, meaning the order in which elements are added is preserved when iterating through the Set. However, this order may not be consistent across different executions of your program.

• new Set(iterable?): Creates a new Set. If you like, you can include an iterable (such as an array) as an argument to populate the Set with initial values.
• .add(value): Adds a new element (value) to the Set. If the element is already there, nothing happens.
• .delete(value): Tries to remove a specific?value?from the Set. Returns?true?if the element was removed,?false?if not.
• .has(value): Checks if a specific?value?is in the Set. Returns?true?if it is,?false?if it's not.
• .size: Gives the number of elements in the Set.
• .clear(): Takes away all elements from the Set.
• The?values(),?keys(), and?entries()?methods return an iterator object for a Set in the order of insertion. Unlike arrays, Sets do not provide direct access to elements by index. Therefore, iteration over a Set is only possible using these three methods and?.forEach().

function findDuplicateElementInArray(numberArray: Array<number>): Array<number>{
  const setArray = new Set(numberArray);
 return numberArray.filter((item) => {
    return !(setArray.delete(item))
 })
}
const number_array = [5, 3, 8, 5]
console.log(findDuplicateElementInArray(number_array))