Question

Here is my code:

 function sort(stack){
  if(stack.length > 0){
   var x = stack.pop();
   sort(stack);
   insert(x,stack);
  }
}
function insert(x,stack){
  if(stack.length>0){
    var tops = topr(stack);
    if(tops>x){
      stack.pop();
      insert(x,stack);
      stack.push(tops);
    }else{
      stack.push(x);
    }
  }
}

function topr(stack){
 var t = stack.pop();
  stack.push(t);
  return t;
}
var stack = [1,3,2];
sort(stack);
console.log(stack);

I had to build this without using an array (recursion).
But it returns void/aka nothing in the console.

Edit:
Full working solution:

function sort(stack) {
    if(stack.length > 0) {
        var x = stack.pop();
        sort(stack);
        insert(x,stack);
    }
    return stack;
}

function insert(x,stack){
  if(stack.length>0){
    var tops = topr(stack);
    if(tops>x){
      stack.pop();
      insert(x,stack);
      stack.push(tops);
    }else{
      stack.push(x);
    }
  }else{
   stack.push(x);
  }
}

function topr(stack){
 var t = stack.pop();
  stack.push(t);
  return t;
}
var stack = [1,3,2];
stack = sort(stack);
console.log(stack);

Answer 1

Because it doesn’t have return stack in its end, perhaps? Without explicit return statement function will return undefined when it completes.

No, it was only the icing on the cake. In fact, there are several logical errors in this code:

• insert() function doesn’t insert a value (x) to an empty stack
• topr() function is confusing. For a non-empty stack, it returns its last element (which can be done more efficiently with just return stack[stack.length - 1], I guess. But if stack is empty, it pushes undefined to it (as it’s a result of pop empty array).