cx.ts

type ClassNameValue = string | number | false | undefined | null | ClassNameValue[] | { [className: string]: boolean }

function cx(...values: ClassNameValue[]) {
  const classNames: string[] = []
  for (const value of values) {
    if (!value) {
      continue
    }

    if (Array.isArray(value)) {
      classNames.push(cx(...value))
      continue
    }

    if (typeof value === 'string' || typeof value === 'number') {
      classNames.push(value.toString())
      continue
    }

    for (const [key, flag] of Object.entries(value)) {
      if (!flag) {
        continue
      }
      classNames.push(key)
    }
  }

  return Array.from(new Set(classNames), c => c.trim()).join(' ')
}

h.ts

function h<K extends keyof HTMLElementTagNameMap>(
  tagName: K,
  attributes: Partial<HTMLElementTagNameMap[K]>,
  children: (Node | null | undefined | string | number | false)[]
): HTMLElementTagNameMap[K] {
  const element = Object.assign(document.createElement(tagName), attributes)

  for (const node of children) {
    if (node == null) {
      continue
    }

    if (node == false) {
      continue
    }

    if (node instanceof Node) {
      element.appendChild(node)
    } else {
      element.innerText = node.toString()
    }
  }

  return element
}