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JavaScript

function cartesian_product(xs, ys) {
    var result = [];
    for(var i = 0; i < xs.length; i++) {
        for (var j = 0; j < ys.length; j++) {
            // transform [ [1, 2], 3 ] => [ 1, 2, 3 ] and append it to result []
            result.push([].concat.apply([], [ xs[i], ys[j] ]));
        }
    }
    return result;
}

function cartesian_power(xs, n) {
    var result = xs;
    for(var i = 1; i < n; i++) {
        result = cartesian_product(result, xs)
    }
    return result;
}
// I need to have 30 numbers in the array and 7 as the second argument, and which is going to be a large number of output.
console.log(cartesian_power([1, 2, 3, 4], 2));