buildHtml.js

const propertyActions = [
  {
    name: 'body',
    check: arg => typeof arg === 'string'
  },
  {
    name: 'children',
    check: arg => arg instanceof Array
  },
  {
    name: 'attributes',
    check: arg => arg instanceof Object
  }
];

const getPropertyAction = arg => propertyActions.find(({ check }) => check(arg));

const buildAttrString = attrs =>
  Object.keys(attrs)
    .map(key => ` ${key}="${attrs[key]}"`)
    .join('');

const buildHtml = data => {
  const [first, ...rest] = data;
  const root = {
    name: first,
    attributes: {},
    body: '',
    children: []
  };
  const tag = rest.reduce((acc, arg) => {
    const { name } = getPropertyAction(arg);
    return { ...acc, [name]: arg };
  }, root);

  return [
    `<${tag.name}${buildAttrString(tag.attributes)}>`,
    `${tag.body}${tag.children.map(buildHtml).join('')}`,
    `</${tag.name}>`
  ].join('');
};

const data = [
  'html',
  [
    ['head', [['title', 'hello, hexlet!']]],
    [
      'body',
      { class: 'container' },
      [
        ['h1', { class: 'header' }, 'html builder example'],
        ['div', [['span'], ['span', { class: 'text', id: 'uniq-key' }]]]
      ]
    ]
  ]
];

console.log(buildHtml(data));