Virtual DOM

const el = (tag, attrs, body) => `${renderTag(tag, attrs)}${renderBody(body)}${renderClosingTag(tag)}`;
const renderTag = (tag, attrs) => `<${tag}${renderAttrs(attrs)}>`;
const renderAttrs = attrs => `${hasAttrs(attrs) ? ' ' : ''}${joinAttrs(attrs)}`;
const hasAttrs = attrs => Object.keys(attrs || {}).length > 0;
const joinAttrs = attrs => Object.entries(attrs).map(attr => attrToString(attr)).join(' ');
const attrToString = ([key, value]) => `${key}="${value}"`;
const renderBody = body => body.join('');
const renderClosingTag = tag => isClosingTag ? `</${tag}>` : '';
const isClosingTag = tag => !tagsWithoutClosing.includes(tag);
const tagsWithoutClosing = ['input'];

const text = txt => txt.toString();
const div = (attrs, ...body) => el('div', attrs, body);
const span = (attrs, ...body) => el('span', attrs, body);