task2.js

var input = [[1, 3], [9,10], [13, 15]];   //input array
try {

    // Iterate through array and complete series, i.e [1, 5] would generate [1, 5, 3, 4, 2]
    input.forEach(tuple => {
        if(tuple.length && tuple[0] != tuple[1]){
            // making sure the code works even when the tuple is not sorted.
            var minimumValue = tuple[0] < tuple[1] ? tuple[0] : tuple[1];
            var maximumValue = tuple[0] > tuple[1] ? tuple[0] : tuple[1];
            // completing series by looping from first tuple - last tuple
            while(minimumValue < maximumValue && (maximumValue - minimumValue != 1)){
                tuple.push(++ minimumValue);
            }
        }else{
            //If empty or same, throw an exception
            throw "empty tuple found or duplicate values in tuple.";
        }
    });

    // Input array with completed series i.e [1, 3, 2], [9, 10], [13, 15, 14]
    console.log(input);

    var stringifiedResult = getCombinations(input, '');
    var finalResult = [];

    // Converting conncatinated string to arrays
    stringifiedResult.forEach(tuple => {
        finalResult.push(tuple.split(","));
    });

    console.log(finalResult);

}catch(err) {
    console.log(err);
}

function getCombinations(array, prefix) {

    prefix = prefix || '';
    if (!array.length) {
        return prefix;
    }

    //Iterate through each element and concatinate while iterating through every array from input array recursively.
    var result = array[0].reduce((result, value) => {
        return result.concat(getCombinations(array.slice(1), prefix ? prefix + ',' + value : prefix + value));
    }, []);

    return result;
}