why doesn't this backtracking recursion go to other branches?

Question

Given an array, and a goal (number), I have to determine if it is possible to reach goal by adding elements from the array. Here is my code (in javascript), and some results:

function check(goal,array) {

  function add(sum, array) {
    if (sum == goal)
      return true;
    else if ((sum > goal)||(!array[0]))
      return false;
    else
        console.log(sum); // check where we are 
      return add(sum + array.shift(),array) || add(sum,array);
  }
  return add(0,array);
}

What I expect to happen to the stack of add() after calling check(6,[1,3,5])

add(0,[1,3,5])   // log 0
    add(1,[3,5])    //log 1  
        add(1+3,[5])    //log 4
            add(1+3+5,[])  //return false
            add(1+3,[])    //return false
        add(1,[5])  //log 1
            add(1+5,[])   //return true
            add(1,[])       

    add[0,[3,5])
        add(0+3,[5])
            add(0+3+5,[])
            add(0+3,[])
        add(0,[5])  
            add(0+5,[])
            add(0,[])

Actual results:

check(6,[1,3,5])
false
0
1
4
check(3,[1,3,5])
false
0
1
1

It never leaves the first branch! Why ? Edit: Ok, based on the suggestions, I guess it's better to avoid passing array as an argument:

function check(goal,array) {

  function add(sum, i) {
    if (sum == goal)
      return true;
    else if ((sum > goal)||(i==array.length))
      return false;
    else
        console.log(sum);
      return add(sum + array[i],i+1) || add(sum,i+1);
  }
  return add(0,0);
}

It works fine here.

Answer 1

It's the same array that's passed around, and after the first branch it'll become empty so the recursion will finish. Try it with a copy:

function check(goal,array) {
    function add(sum, array) {
        if (sum == goal)
            return true;
        else if ((sum > goal)||(!array[0]))
            return false;
        else
            print(sum);
        array = array.slice();
        return add(sum + array.shift(),array) || add(sum,array);
    }
    return add(0,array);
}