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

var delim = {'a': 1};

​

function spreadArrayComparisonAndConcat(array, delim) {

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

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

    }, []);

}

​

function spreadArrayConcat(array, delim) {

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

        return result.concat(delim, item);

    }, []).slice(0, -1);

}

​

function spreadArrayComparison(array, delim) {

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

         if (i === 0) {

           result.push(item);

         } else {

           result.push(delim, item);

         }

        return result;

    }, []);

}

​

function spreadArrayComparisonArrow(array, delim) {

    return array.reduce((result, item, i) => {

         if (i === 0) {

           result.push(item);

         } else {

           result.push(delim, item);

         }

        return result;

    }, []);

}

​

function spreadArrayPop(array, delim) {

    var r = array.reduce(function (result, item) {

        result.push(item, delim);      

        return result;

    }, []);

    r.pop();

    return r;

}

​

function spreadArrayShift(array, delim) {

    var r = array.reduce(function (result, item) {

        result.push(delim, item);      

        return result;

    }, []);

    r.shift();

    return r;

}

​

function spreadArraySlice(array, delim) {

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

        result.push(delim, item);      

        return result;

    }, []).slice(1);

}

​

function spreadArrayTailSlice(array, delim) {

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

        result.push(delim, item);

        return result;

    }, []).slice(0, -1);

}

​

function spreadArraySlice2(array, delim) {

    return array.slice(1).reduce(function (result, item) {

        result.push(delim, item);      

        return result;

    }, []);

}

​

​

function spreadArrayFor(arr, delim) {

    var result = [];

    for (var i = 0; i < arr.length; i++) {

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

    };

    result.pop();

    return result;

}

​

function spreadArrayForReverse(arr, delim) {

    var result = []

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

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

    };

    result.pop();

    return result;

}

​

function spreadArrayForComparison(arr, delim) {

    var result = [];

    for (var i = 0; i < arr.length; i++) {

        if (i === 0) {

          result.push(arr[i]);

        } else {

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

        }

    };

    return result;

}

​

function spreadArrayForWithInit(arr, delim) {

    var result = [arr[0]]

    for (var i = 1; i < arr.length; i++) {          

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

    };

    return result;

}

​