const allEqual = arr => arr.every(v => v === arr[0]);

allEqual([1,1,1,1]);  // true

const areEqual = (arr1, arr2) =>

  arr1.sort().join(',') === arr2.sort().join(',');

const arr1 = [1, 2, 3, 4];

const arr2 = [3, 4, 1, 2];

const arr3 = [1, 2, 3];

console.log(areEqual(arr1, arr2)); // true

console.log(areEqual(arr1, arr3)); // false

function hasDuplicates(array) {

  // create a set to store unique values

  const uniqueValues = new Set();

​

  // loop through the array

  for (let i = 0; i < array.length; i++) {

    // if the value is not in the set, add it

    if (!uniqueValues.has(array[i])) {

      uniqueValues.add(array[i]);

    } else {

      // if the value is already in the set, return true

      return true;

    }

  }

​

  // if the loop completes and there are no duplicates, return false

  return false;

}

​

const numbers = [1, 2, 3, 4, 5];

const hasDuplicates = hasDuplicates(numbers); // returns false

​

const letters = ['a', 'b', 'c', 'b'];

const hasDuplicates = hasDuplicates(letters); // returns true

const allEqual = arr => arr.every( v => v === arr[0] )

allEqual( [1,1,1,1] )  // true