共通のコンポーネント使っててpath別で処理したいときあるよね。
必要な度にググってるのでメモ。

だめな例

SSRされたときはdocumentがないので下記ではだめ。

pages/my-component.js

import React from 'react';

const MyComponent = props => {
  console.log(document.location);
...

Server Error
ReferenceError: document is not defined

This error happened while generating the page. Any console logs will be displayed in the terminal window.

だめな例２

client sideで使えって怒られた

pages/my-component.js

import React from 'react';
import Router from 'next/router';

const MyComponent = props => {
  console.log(Router.pathname);
...

Server Error
Error: No router instance found.
You should only use "next/router" inside the client side of your app.

いい例

hookが提供されてるからこれ使おう

pages/my-component.js

import React from 'react';
import { useRouter } from 'next/router';

const MyComponent = props => {
  const router = useRouter();
  console.log(router.pathname); // '/example/mycomponent'
...

参考

next/router | Next.js - https://nextjs.org/docs/api-reference/next/router