algorithm - All Array Combination in JavaScript

Question

Need all possible combinations of an array including the reverse of a combination too.

Eg:

var b = ['a1','b1','a','b'];

Need combinations as:

a1,b1,a,b
a1b1,a1a,a1b, b1a1,b1a,b1b, ......,
a1b1a,a1b1b,a1ab1,a1bb1,........,
a1b1ab,a1b1ba.....bab1a1

All 64 combinations (if array has 4 elements). I found solution in java using ArrayList and Collection API, but right now I need a pure JavaScript ES5 solution.

I tried the following, but it only provides lesser combinations.

function getCombinations(chars) {
    var result = [];
    var f = function (prefix, chars) {
        for (var i = 0; i < chars.length; i++) {
            result.push(prefix + chars[i]);
            f(prefix + chars[i], chars.slice(i + 1));
        }
    }
    f('', chars);
    return result;
}

Answer 1

Let's put your request into words: for each starting element, append all permutations of all combinations of the rest of the elements.

function f(A, comb=[], result=[comb]){
  return A.reduce((acc, a, i) => acc.concat(f(A.slice(0,i).concat(A.slice(i+1)), comb.concat(a))), result);
}

console.log(JSON.stringify(f(['a', 'b', 'c', 'd'])));