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next.js/packages/next-server/lib/head.js

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import React from 'react'
import PropTypes from 'prop-types'
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import sideEffect from './side-effect'
class Head extends React.Component {
static contextTypes = {
headManager: PropTypes.object
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}
render () {
return null
}
}
const NEXT_HEAD_IDENTIFIER = 'next-head'
export function defaultHead (className = NEXT_HEAD_IDENTIFIER) {
return [
<meta key='charSet' charSet='utf-8' className={className} />
]
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}
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function reduceComponents (components) {
return components
.map((component) => React.Children.toArray(component.props.children))
.reduce((a, b) => a.concat(b), [])
.reduce((a, b) => {
if (React.Fragment && b.type === React.Fragment) {
return a.concat(React.Children.toArray(b.props.children))
}
return a.concat(b)
}, [])
.reverse()
.concat(defaultHead(''))
.filter(Boolean)
.filter(unique())
.reverse()
.map((c, i) => {
const className = (c.props && c.props.className ? c.props.className + ' ' : '') + NEXT_HEAD_IDENTIFIER
const key = c.key || i
return React.cloneElement(c, { key, className })
})
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}
function mapOnServer (head) {
return head
}
function onStateChange (head) {
if (this.context && this.context.headManager) {
this.context.headManager.updateHead(head)
}
}
const METATYPES = ['name', 'httpEquiv', 'charSet', 'itemProp', 'property']
const ALLOWED_DUPLICATES = ['article:tag', 'og:image', 'og:image:alt', 'og:image:width', 'og:image:height', 'og:image:type', 'og:image:secure_url', 'og:image:url']
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/*
returns a function for filtering head child elements
which shouldn't be duplicated, like <title/>,
except we explicit allow it in ALLOWED_DUPLICATES array
*/
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function unique () {
const keys = new Set()
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const tags = new Set()
const metaTypes = new Set()
const metaCategories = {}
return (h) => {
if (h.key && h.key.indexOf('.$') === 0) {
if (keys.has(h.key)) return false
keys.add(h.key)
}
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switch (h.type) {
case 'title':
case 'base':
if (tags.has(h.type)) return false
tags.add(h.type)
break
case 'meta':
for (let i = 0, len = METATYPES.length; i < len; i++) {
const metatype = METATYPES[i]
if (!h.props.hasOwnProperty(metatype)) continue
if (metatype === 'charSet') {
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if (metaTypes.has(metatype)) return false
metaTypes.add(metatype)
} else {
const category = h.props[metatype]
const categories = metaCategories[metatype] || new Set()
if (categories.has(category) && ALLOWED_DUPLICATES.indexOf(category) === -1) return false
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categories.add(category)
metaCategories[metatype] = categories
}
}
break
}
return true
}
}
export default sideEffect(reduceComponents, onStateChange, mapOnServer)(Head)