index.js

'use strict'

const m = require('mithril/hyperscript')
const Vnode = require('mithril/render/vnode')

const VOID_TAGS = new RegExp(
  '^(?:' +
    'area|' +
    'base|' +
    'br|' +
    'col|' +
    'command|' +
    'embed|' +
    'hr|' +
    'img|' +
    'input|' +
    'keygen|' +
    'link|' +
    'meta|' +
    'param|' +
    'source|' +
    'track|' +
    'wbr|' +
    '!doctype' +
    ')$',
  'i'
)

const hasOwn = {}.hasOwnProperty

function toStyleKey(str) {
  if (str[0] === '-' && str[1] === '-') {
    return str
  }
  return str
    .replace(/\W+/g, '-')
    .replace(/([a-z\d])([A-Z])/g, '$1-$2')
    .toLowerCase()
}

function replaceHtml(m) {
  if (m === '&') return '&'
  if (m === '<') return '&lt;'
  return '&gt;'
}

function replaceAttribute(m) {
  if (m === '&') return '&amp;'
  if (m === '<') return '&lt;'
  if (m === '>') return '&gt;'
  return '&quot;'
}

const defaults = {
  escapeText(s) {
    return s.replace(/[&<>]/g, replaceHtml)
  },

  escapeAttribute(s) {
    return s.replace(/[&<>"]/g, replaceAttribute)
  },
}

function bindOpt(options, key) {
  return options[key] ? options[key].bind(options) : defaults[key]
}

// Using a generator so I can just yield promises that need awaited. Can't just
// use `async`/`await` since this is used for both sync and async renders. At
// least I have generators (read: coroutines), or I'd have to implement this
// using a giant pushdown automaton. :-)
function* tryRender(view, attrs, options, allowAwait) {
  // Fast-path a very simple case. Also lets me perform some renderer
  // optimizations later.
  if (view == null) return ''
  if (view.view || typeof view === 'function') {
    // root component
    view = m(view, attrs)
    options = options || {}
  } else {
    options = attrs || {}
  }
  const hooks = []
  let result = ''
  const escapeAttribute = bindOpt(options, 'escapeAttribute')
  const escapeText = bindOpt(options, 'escapeText')
  const xml = !!options.xml
  const strict = xml || !!options.strict

  function write(value) {
    result = '' + result + value
  }

  function* setHooks(source, vnode) {
    const promises = []
    let waitFor
    if (allowAwait)
      waitFor = p => {
        promises.push(p)
      }
    if (source.oninit) {
      source.oninit.call(vnode.state, vnode, waitFor)
    }
    if (source.onremove) {
      hooks.push(source.onremove.bind(vnode.state, vnode))
    }
    if (promises.length) yield promises
  }

  function createAttrString(view) {
    for (const key in view.attrs) {
      if (hasOwn.call(view.attrs, key)) {
        let value = view.attrs[key]
        if (value == null || typeof value === 'function') continue
        const name = key === 'className' ? 'class' : key

        if (name === 'style' && typeof value === 'object') {
          const styles = value
          const props = []
          for (const key of Object.keys(styles)) {
            const prop = styles[key]
            if (prop) props.push(`${toStyleKey(key)}:${prop}`)
          }
          if (!props.length) continue
          value = props.join(';')
        }

        if (typeof value === 'boolean') {
          if (xml) value = value ? 'true' : 'false'
          else if (!value) continue
          else value = ''
        } else {
          value = '' + value
        }

        write(` ${name}`)
        if (strict || value !== '') {
          write(`="${escapeAttribute(value)}"`)
        }
      }
    }
  }

  function* renderComponent(vnode) {
    if (typeof vnode.tag !== 'function') {
      vnode.state = Object.create(vnode.tag)
    } else if (vnode.tag.prototype && vnode.tag.prototype.view) {
      vnode.state = new vnode.tag(vnode)
    } else {
      vnode.state = vnode.tag(vnode)
    }

    yield* setHooks(vnode.state, vnode)
    if (vnode.attrs != null) yield* setHooks(vnode.attrs, vnode)
    vnode.instance = Vnode.normalize(vnode.state.view(vnode))
    if (vnode.instance != null) yield* renderNode(vnode.instance)
  }

  function* renderElement(vnode) {
    write(`<${vnode.tag}`)
    createAttrString(vnode)
    // Don't write children for void HTML elements
    if (!xml && VOID_TAGS.test(vnode.tag)) {
      write(strict ? '/>' : '>')
    } else {
      write('>')
      if (vnode.text != null) {
        const text = '' + vnode.text
        if (text !== '') write(escapeText(text))
      } else {
        yield* renderChildren(vnode.children)
      }
      write(`</${vnode.tag}>`)
    }
  }

  function* renderChildren(vnodes) {
    for (const v of vnodes) {
      if (v != null) yield* renderNode(v)
    }
  }

  function* renderNode(vnode) {
    if (vnode == null) return
    if (typeof vnode.tag === 'string') {
      vnode.state = {}
      if (vnode.attrs != null) yield* setHooks(vnode.attrs, vnode)
      switch (vnode.tag) {
        case '#':
          write(escapeText('' + vnode.children))
          break
        case '<':
          write(vnode.children)
          break
        case '[':
          yield* renderChildren(vnode.children)
          break
        default:
          yield* renderElement(vnode)
      }
    } else {
      yield* renderComponent(vnode)
    }
  }

  yield* renderNode(Vnode.normalize(view))
  for (const hook of hooks) hook()
  return result.concat() // hint to flatten
}

module.exports = async (view, attrs, options) => {
  const iter = tryRender(view, attrs, options, true)
  // eslint-disable-next-line no-constant-condition
  while (true) {
    const { done, value } = iter.next()
    if (done) return value
    await Promise.all(value)
  }
}

module.exports.sync = (view, attrs, options) => {
  return tryRender(view, attrs, options, false).next().value
}

module.exports.escapeText = defaults.escapeText
module.exports.escapeAttribute = defaults.escapeAttribute