var testArray = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');

var delim = {'a': 1};

​

function spreadArrayErtema(array, delim) {

    return array.reduce(function (result, item, i) {

        return i === 0 ? result.concat(item) : result.concat(delim, item);

    }, []);

}

​

function spreadArrayKbakba(arr, delim) {

    var result = []

    for (var i = arr.length - 1; i >= 0; i--) {

        result.unshift(arr[i], delim);

    };

    result.pop();

    return result;

}

​