SOURCE

let arr = [47916,47916,47917,47920,47920,47921,47922,47923,47931,47931,47932,47933];
arr = [47938,47937,47933,47932,47931,47931,47923,47922,47921,47920,47920,47917,47916,47916];
console.log(arr.length);

arr.forEach((item, index) => {
    if (index > 0) {
        if (item == arr[index-1]) {
            arr.splice(index, 1)
        }
    }
})

console.log(arr)
console.log(arr.length);