Please explain what the following code does in react java script

Main.js file:

import express from "express";

import ListRouter from $"./$list$.$js$"$;

import $\{$ MongoClient $\}$ from "mongodb";

import cors from "cors";

import ProsRouter from $"./$ps$.$js$"$;

async function connect$()\{$

const client $=$ new MongoClient$("$mongodb:$//$localhost:$27018")$;

const connection $=$ await client.connect$()$;

return connection.db$("$spa$-$database"$)$;

$\}$

const port $=3000$;

const app $=$ express$()$;

app.use$($cors$())$;

app.use$($express$.$json$())$;

app.use$("/$ps$",$ ProsRouter$)$;

app.use$("/$list$",$ ListRouter$)$;

const database $=$ await connect$()$;

app.set$("$db$",$ database$)$;

Pros.js file:

import $\{$ Router $\}$ from "express";

import $\{$ ObjectId $\}$ from "mongodb";

import ListRouter from $"./$list$.$js$"$;

const ProsRouter $=$ Router$()$;

ProsRouter.use$("/$:pId$/$list$",$ ListRouter$)$;

ProsRouter.get$("/",$ async $($req$,$ res$)=>\{$

const db $=$ req.app.get$("$db$")$;

const list $=$ await db$.$collection$("$ps$").$find$().$toArray$()$;

return res.json$($list$)$;

$\})$;

ProsRouter.get$("/$:id$",$ async $($req$,$ res$)=>\{$

const db $=$ req.app.get$("$db$")$;

const todo $=$ await db$.$collection$("$ps$").$findOne$(\{\_$id: new ObjectId$($req$.$params.id$)\})$;

return res.json$($todo$)$;

$\})$;

ProsRouter.post$("/",$ async $($req$,$ res$)=>\{$

const db $=$ req.app.get$("$db$")$;

try $\{$

const result $=$ await db$.$collection$("$ps$").$insertOne$($req$.$body$)$;

console.info$($result$)$;

res.status$(200).$json$($result$.$insertedId$)$;

$\}$ catch $($e$)\{$

console.error$($e$)$;

return res.status$(500).$end$()$;

$\}$

$\})$;

ProsRouter.put$("/$:id$",$ async $($req$,$ res$)=>\{$

req.body.$\_$id $=$ new ObjectId$($req$.$params.id$)$;

const db $=$ req.app.get$("$db$")$;

try $\{$

const updateResult $=$ await db$.$collection$("$ps$").$update$(\{\_$id: new ObjectId$($req$.$params.id$)\},$ req.body$)$;

console.info$($updateResult$)$;

$\}$ catch $($e$)\{$

console.error$($e$)$;

return res.status$(500).$end$()$;

$\}$

return res.status$(200).$end$()$;

$\})$;

ProsRouter.delete$("/$:id$",$ async $($req$,$ res$)=>\{$

const db $=$ req.app.get$("$db$")$;

try $\{$

await db$.$collection$("$ps$").$deleteOne$(\{\_$id: new ObjectId$($req$.$params.id$)\})$;

$\}$ catch $($e$)\{$

console.error$($e$)$;

return res.status$(500).$end$()$;

$\}$

return res.status$(200).$end$()$;

$\})$;

export default ProsRouter;

list.js file:

import $\{$ Router $\}$ from "express";

const ListRouter $=$ Router$()$;

ListRouter.mergeParams $=$ true;

ListRouter.get$("/$:todoId", $($req$,$ res$)=>\{$

console.log$($req$.$params$)$;

res.status$(200).$json$(\{$

name: "Some new todo",

description: $"$Do all the things and render it well",

completed: false,

p$\_$id: req.params.pId,

$\}).$end$()$;

$\})$;

export default ListRouter;