How can I find all the sum of combinations of elements in an array

Question

I am white boarding on how to solve Coin/Change Problem. Given a set of coins (array of numbers) [1,2,3] find all the combinations that can add up to the given amount/target. I understand the logic. The indexes of the array has to find all possible combinations that adds to the target, and so on. I am having trouble with this can someone guide me through. How should I go about white boarding this question? 1,1,1,1,1 1,1,1,2 1,2,2 1,1,3 2, 3

function coin(amount, array) {

  var results = [], result = [], total = 0;

  if (array.length === 0) {
    return results; 
  } 

  if ( amount <= 0) {
    return 'Enter an amount';
  }

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



    return coin(amount, array.slice(1));
  }

}

coin(5,[1,2,3]);