Has No Duplicates

Has No Duplicates numbers are numbers that cannot have duplicates, if there are duplicates we return false else we return true

Example:
console.log(hasNoDuplicates([1,0,2,3,4,4])) false
console.log(hasNoDuplicates([1,2,3,4,5,6])) true

function hasNoDuplicates(arr){
  return arr.every(function(val){
    return arr.indexOf(val) === arr.lastIndexOf(val)
  })
}

console.log(hasNoDuplicates([1,0,2,3,4,4])) false
console.log(hasNoDuplicates([1,2,3,4,5,6])) true

We create a function called hasNoDuplicates with parameter called arr

We return the arr.every every is build in JavaScript method that needs all to be true from the array or not;

We return arr.every(function(val){
return arr.indexOf(val) === arr.lastIndexOf(val)
After returning .every we have callback function with paramerer val and we return the indexOf which is JavaScript method The indexOf() method returns the first index at which a given element can be found in the array, or -1 if it is not present. -MDN

To be equal to arr.lastIndexOf(val) which is another JavaScript method The lastIndexOf() method returns the last index at which a given element can be found in the array, or -1 if it is not present. The array is searched backwards, starting at fromIndex. -MDN

If indexOf and lastIndexOf the parameter val are found in both of the methods it returns false; if every index is different is returns true;