how to check if an array is sorted ascending or descending alphabetically or unsorted.
["apple","summer","sun","zoo"] // ascending
You can iterate over the array and track the results of String#localeCompare() called on all neighbors.
Then simply check if all results are either <= 0 or >=0 and return 'ascending' or 'descending' accordingly, otherwise return 'unsorted'.
function getSortDirection(arr) {
const c = [];
for (let i = 1; i < arr.length; i++) {
c.push(arr[i - 1].localeCompare(arr[i]));
}
if (c.every((n) => n <= 0)) return 'ascending';
if (c.every((n) => n >= 0)) return 'descending';
return 'unsorted';
}
const ascending = ['apple', 'summer', 'sun', 'zoo'];
const descending = ['zoo', 'sun', 'summer', 'apple'];
const unsorted = ['summer', 'zoo', 'apple', 'sun'];
console.log(ascending, '–', getSortDirection(ascending));
console.log(descending, '–', getSortDirection(descending));
console.log(unsorted, '–', getSortDirection(unsorted));You could check the item with the previous item or return true for the first item.
const
asc = (b, i, { [i - 1]: a }) => !i || a <= b,
array = ["apple", "summer", "sun", "zoo"];
console.log(array.every(asc));