Javascript check if items in an array are consecutive

Question

Say I have an array which holds the values [1,2,3,6,7].

How can I check the array to see if it holds 3 consecutive numbers. For example, the array above holds [1,2,3] so this would return false in my function.

        var currentElement = null;
        var counter = 0;

        //check if the array contains 3 or more consecutive numbers:
        for (var i = 0; i < bookedAppArray.length; i++) {
            if ((bookedAppArray[i] != currentElement) && (bookedAppArray[i] === bookedAppArray[i - 1] + 1)) {

                if (counter > 2) {
                    return true;
                }

                currentElement = bookedAppArray[i];
                counter++;
            } else {
                counter = 1;
            }
        }

        if(counter > 2){
            return true;
        } else{
            return false;
        }

Answer 1

This solution

• checks wheater the length of the array is greater than 2,
• iterates over the array from position 2
• gets the difference between position 2 and 1 before the index,
• checks if the absolute difference is 1
• checks the difference between position 1 before and at the index is equal the difference,
• and if so, it returns false, because consecutive elements are found.
• if not, increment index by 1

function consecutive(array) {
    var i = 2, d;
    while (i < array.length) {
        d = array[i - 1] - array[i - 2];
        if (Math.abs(d) === 1 && d === array[i] - array[i - 1]) {
            return false;
        }
        i++;
    }
    return true;
}

document.write(consecutive([1]) + '<br>');             // true
document.write(consecutive([2, 4, 6]) + '<br>');       // true
document.write(consecutive([9, 8, 7]) + '<br>');       // false
document.write(consecutive([1, 2, 3, 6, 7]) + '<br>'); // false
document.write(consecutive([1, 2, 3, 4, 5]) + '<br>'); // false