vue-meta/src/shared/getMetaInfo.js

import { findIndex } from '../utils/array'
import { escapeMetaInfo } from '../shared/escaping'
import { applyTemplate } from './template'

/**
 * Returns the correct meta info for the given component
 * (child components will overwrite parent meta info)
 *
 * @param  {Object} component - the Vue instance to get meta info from
 * @return {Object} - returned meta info
 */
export default function getMetaInfo (options, info, escapeSequences, component) {
  options = options || {}
  escapeSequences = escapeSequences || []

  const { tagIDKeyName } = options
  // Remove all "template" tags from meta

  // backup the title chunk in case user wants access to it
  if (info.title) {
    info.titleChunk = info.title
  }

  // replace title with populated template
  if (info.titleTemplate && info.titleTemplate !== '%s') {
    applyTemplate({ component, contentKeyName: 'title' }, info, info.titleTemplate, info.titleChunk || '')
  }

  // convert base tag to an array so it can be handled the same way
  // as the other tags
  if (info.base) {
    info.base = Object.keys(info.base).length ? [info.base] : []
  }

  if (info.meta) {
    // remove meta items with duplicate vmid's
    info.meta = info.meta.filter((metaItem, index, arr) => {
      const hasVmid = !!metaItem[tagIDKeyName]
      if (!hasVmid) {
        return true
      }

      const isFirstItemForVmid = index === findIndex(arr, item => item[tagIDKeyName] === metaItem[tagIDKeyName])
      return isFirstItemForVmid
    })

    // apply templates if needed
    info.meta.forEach(metaObject => applyTemplate(options, metaObject))
  }

  return escapeMetaInfo(options, info, escapeSequences)
}