Find combinations of a list of arrays [ ['a], ['b'] ] = 'a' 'b' 'ab'

combinations

function getCombinations( list ) {
    var set = [],
        listSize = list.length,
        combinationsCount = (1 << listSize),
        combination;

    for ( var i = 1; i < combinationsCount; i++ ) {
        var combination = [];
        for ( var j=0; j<listSize; j++ ) {
            if ( (i & (1 << j)) ) {
                combination.push( list[j] );
            }
        }
        set.push(combination);
    }

    return set;
}