Shows error when res.json and next are both called.

console.txt

% node middleware.js                                                   130 ↵
Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:344:11)
    at ServerResponse.header (/usr/local/lib/node_modules/express/lib/response.js:718:10)
    at ServerResponse.send (/usr/local/lib/node_modules/express/lib/response.js:163:12)
    at ServerResponse.json (/usr/local/lib/node_modules/express/lib/response.js:249:15)
    at /Users/phil/Desktop/middleware.js:20:6
    at Layer.handle [as handle_request] (/usr/local/lib/node_modules/express/lib/router/layer.js:95:5)
    at trim_prefix (/usr/local/lib/node_modules/express/lib/router/index.js:312:13)
    at /usr/local/lib/node_modules/express/lib/router/index.js:280:7
    at Function.process_params (/usr/local/lib/node_modules/express/lib/router/index.js:330:12)
    at next (/usr/local/lib/node_modules/express/lib/router/index.js:271:10)

middleware.js

'use strict';
const express = require('express');
const app = express();

const somethingThatFailed = false;

app.use((req, res, next) => {
	if (somethingThatFailed){
		console.log("Error here");
	}else{
		res.json({A: 1});	
	}
	next();
});

app.use((req, res, next) => {
	res.json({A: 2});
});

app.listen(3000);