第 16 章　从做完到交付

function addItem() {
  var name = document.getElementById('name').value;
  var count = Number(document.getElementById('count').value);   // 填“三十”得到 NaN
  items.push({ name: name, count: count });                     // 不检查就存
  console.log('添加了一条', name, count, items);                  // 调试残留，见 16.5
  render();
}

function render() {
  var sum = 0;
  for (var i = 0; i < items.length; i++) {
    …
    sum = sum + items[i].count;                                 // NaN 一参与，合计就是 NaN
  }
  var names = items.map(function (it) { return it.name; });
  var joined = names.slice(0, -1).join('、') + ' 和 ' + names[names.length - 1];
  document.getElementById('total').textContent =
    '已录入 ' + joined + '，共 ' + items.length + ' 项，合计 ' + sum + ' 人。';
  console.log('当前合计', sum);
}