map over arr, group seq identical items together

function recurCheck (arr, index) {
    let flag = true;
    let localIndex = index;
    for (i = localIndex; flag === true;) {
        if (arr[localIndex + 1] === arr[index]) {
            localIndex++
        }
        else {
            flag = false;
        }
    }
    return {start: index, stop: localIndex}
}

function arrStartStop (arr) {
    let checkForNestedArr = arr.filter(item => Array.isArray(item));

    if (checkForNestedArr.length) {

        return "nested array"
    }

        let newArr = [];
        for (i = 0; i < arr.length; i++) {
            newArr.push(recurCheck(arr, i));
        }

        return newArr.map((obj, index) => {
            if (obj.start !== obj.stop) {
                let localArr = [];
                for (i = 0; i < (obj.stop - obj.start + 1); i++) {
                    localArr.push(arr[obj.stop]);
                }
                return localArr;
            }
            else {
                if (obj.stop !== newArr[index - 1].stop) {
                    return [arr[obj.stop]];
                }
            }
        })
        .filter(item => item !== undefined)


}

arrStartStop([1, 1, 2, 1, 1, 1, 3, 3])
arrStartStop(["a", "a", "b", "b", "c"])
arrStartStop([[1, 2], [1, 2], [3, 4]])