src/compiler/transclude.js

var _ = require('../util')
var config = require('../config')
var templateParser = require('../parsers/template')

/**
 * Process an element or a DocumentFragment based on a
 * instance option object. This allows us to transclude
 * a template node/fragment before the instance is created,
 * so the processed fragment can then be cloned and reused
 * in v-repeat.
 *
 * @param {Element} el
 * @param {Object} options
 * @return {Element|DocumentFragment}
 */

exports.transclude = function (el, options) {
  // extract container attributes to pass them down
  // to compiler, because they need to be compiled in
  // parent scope. we are mutating the options object here
  // assuming the same object will be used for compile
  // right after this.
  if (options) {
    options._containerAttrs = extractAttrs(el)
  }
  // for template tags, what we want is its content as
  // a documentFragment (for block instances)
  if (_.isTemplate(el)) {
    el = templateParser.parse(el)
  }
  if (options) {
    if (options._asComponent && !options.template) {
      options.template = '<content></content>'
    }
    if (options.template) {
      options._content = _.extractContent(el)
      el = transcludeTemplate(el, options)
    }
  }
  if (el instanceof DocumentFragment) {
    // anchors for block instance
    // passing in `persist: true` to avoid them being
    // discarded by IE during template cloning
    _.prepend(_.createAnchor('v-start', true), el)
    el.appendChild(_.createAnchor('v-end', true))
  }
  return el
}

/**
 * Process the template option.
 * If the replace option is true this will swap the $el.
 *
 * @param {Element} el
 * @param {Object} options
 * @return {Element|DocumentFragment}
 */

function transcludeTemplate (el, options) {
  var template = options.template
  var frag = templateParser.parse(template, true)
  if (frag) {
    var replacer = frag.firstChild
    var tag = replacer.tagName && replacer.tagName.toLowerCase()
    if (options.replace) {
      /* istanbul ignore if */
      if (el === document.body) {
        process.env.NODE_ENV !== 'production' && _.warn(
          'You are mounting an instance with a template to ' +
          '<body>. This will replace <body> entirely. You ' +
          'should probably use `replace: false` here.'
        )
      }
      if (
        // multi-children template
        frag.childNodes.length > 1 ||
        // non-element template
        replacer.nodeType !== 1 ||
        // when root node is <component>, is an element
        // directive, or has v-repeat, the instance could
        // end up having multiple top-level nodes, thus
        // becoming a block instance.
        tag === 'component' ||
        _.resolveAsset(options, 'elementDirectives', tag) ||
        replacer.hasAttribute(config.prefix + 'repeat')
      ) {
        return frag
      } else {
        options._replacerAttrs = extractAttrs(replacer)
        mergeAttrs(el, replacer)
        return replacer
      }
    } else {
      el.appendChild(frag)
      return el
    }
  } else {
    process.env.NODE_ENV !== 'production' && _.warn(
      'Invalid template option: ' + template
    )
  }
}

/**
 * Helper to extract a component container's attribute names
 * into a map.
 *
 * @param {Element} el
 * @return {Object}
 */

function extractAttrs (el) {
  if (el.nodeType === 1 && el.hasAttributes()) {
    var attrs = el.attributes
    var res = {}
    var i = attrs.length
    while (i--) {
      res[attrs[i].name] = attrs[i].value
    }
    return res
  }
}

/**
 * Merge the attributes of two elements, and make sure
 * the class names are merged properly.
 *
 * @param {Element} from
 * @param {Element} to
 */

function mergeAttrs (from, to) {
  var attrs = from.attributes
  var i = attrs.length
  var name, value
  while (i--) {
    name = attrs[i].name
    value = attrs[i].value
    if (!to.hasAttribute(name)) {
      to.setAttribute(name, value)
    } else if (name === 'class') {
      to.className = to.className + ' ' + value
    }
  }
}