prefetch.js

import React from 'react'
import Link from './link'
import Router from './router'
import { warn, execOnce } from './utils'

const warnImperativePrefetch = execOnce(() => {
  const message = '> You are using deprecated "next/prefetch". It will be removed with Next.js 2.0.\n' +
    '> Use "Router.prefetch(href)" instead.'
  warn(message)
})

const wantLinkPrefetch = execOnce(() => {
  const message = '> You are using deprecated "next/prefetch". It will be removed with Next.js 2.0.\n' +
    '> Use "<Link prefetch />" instead.'
  warn(message)
})

export function prefetch (href) {
  warnImperativePrefetch()
  return Router.prefetch(href)
}

export default class LinkPrefetch extends React.Component {
  render () {
    wantLinkPrefetch()
    const props = {
      ...this.props,
      prefetch: this.props.prefetch !== false
    }

    return (<Link {...props} />)
  }
}