.js

// entities = { next: linkedListItem, size: numberOfItems }
// linkedListItem = { isDeleted: true/false, next: linkedListItem }

var cur = entities;
for (var i = 0; i < entities.size; i++) {
  if (cur.next.value < 0) {
    cur.next = cur.next.next;
    // bug is that we increase i AND decrease entities.size, which
    // causes us to approach the end of the loop from both sides
    entities.size--;
  } else {
    cur = cur.next;
  }
}

test.js

function constructList(arr) {
  var entities = { next: null, size: 0 };
  var cur = entities;
  arr.forEach(v => {
    var obj = { value: v, next: null };
    cur.next = obj;
    cur = cur.next;
    entities.size++;
  });
  return entities;
}

// negative values are considered deleted
function brokenRemoveDeleted(entities) {
  var cur = entities;
  for (var i = 0; i < entities.size; i++) {
    if (cur.next.value < 0) {
      cur.next = cur.next.next;
      entities.size--;
    } else {
      cur = cur.next;
    }
  }
}

function printResults(entities) {
  var results = [], item = entities.next;
  while (item !== null) {
    results.push(item.value);
    item = item.next;
  }
  console.log(results);
}

// test([n, ....])
function test(arr) {
  var entities = constructList(arr);
  var size, newSize;
  do {
    size = entities.size;
    printResults(entities);
    brokenRemoveDeleted(entities);
    newSize = entities.size;
  } while (size !== newSize);
}

test([-1, -2, -3, -4, -5].reverse());
test([-1, 1, -2, 1, 1, 1, -3, -4, -5, -6, -7, -8].reverse());