get all combinations for a string

This is a recursive solution that I think is very easy to understand.

var tree = function(leafs) {
  var branches = [];
  if (leafs.length == 1) return leafs;
  for (var k in leafs) {
    var leaf = leafs[k];
    tree(leafs.join('').replace(leaf, '').split('')).concat("").map(function(subtree) {
      branches.push([leaf].concat(subtree));
    });
  }
  return branches;
};
console.log(tree("abc".split('')).map(function(str) {
  return str.join('')
}))

You could use a nasty trick and increase a counter and use its binary representation as flags:

 function combine(str){
   const result = [];
   for(let i = 1; i < Math.pow(2, str.length) - 1; i++)
      result.push([...str].filter((_, pos) => (i >> pos) & 1).join(""));
  return result;
}

Try it

This is what I ended up using.

var combinations = function (string)
{
    var result = [];

    var loop = function (start,depth,prefix)
    {
        for(var i=start; i<string.length; i++)
        {
            var next = prefix+string[i];
            if (depth > 0)
                loop(i+1,depth-1,next);
            else
                result.push(next);
        }
    }

    for(var i=0; i<string.length; i++)
    {
        loop(0,i,'');
    }

    return result;
}