random-image.js

const express = require("express");
const fs = require("fs");
const app = express();

function isValidURL(string) {
  var res = string.match(/(http(s)?:\/\/.)?(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)/g);
  return (res !== null && string.includes(".gif"))
};

app.get("/api/pika/", (req, res) => {
  let pika = JSON.parse(fs.readFileSync(__dirname + "/public/pika.json"));
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Headers", "X-Requested-With");
  if (req.query.url) {
    if (!isValidURL(req.query.url)) return res.send("This is not a valid image url.")
    if (yourArray.indexOf("someString") > -1) return res.send("This url is already in the database.")
    pika.push(req.query.url)
    fs.writeFileSync(
      __dirname + "/public/pika.json",
      JSON.stringify(pika)
    );
    console.log(req.query.url, "has been submitted")
    res.send("Thank you for your submission of " + req.query.url + ". It will be reviewed shortly.")
    return;
  }
  let num = Math.round(Math.random() * pika.length);
  res.json({ image: pika[num] });
});

app.get("/api/pika.gif", (req, res) =>{
    let num = Math.round(Math.random() * pika.length);
    req.pipe(request(pika[num]).on("response", remoteRes => {
    // You can add/remove/modify headers here
    remoteRes.headers["cache-control"] = 'public, max-age=7884000';
  })).pipe(res);
})

let listener = app.listen(process.env.PORT, () => {
  console.log(
    "❗ Your app has restarted and is listening on port " +
    listener.address().port
  );
});