How do I import multiple objects/components/interfaces using the least amount of require() syntax? For example, the es6 code has this,
import express, {Express, Request, Response} from "express";
Is there something similar I can do using the require() module? Thanks in advance.
You can do something like
const express = require("express");
const {Express, Request, Response} = express;
If you don't need the express, you can do
const {Express, Request, Response} = require("express");
Choose the one that suits you better
Related
What is the best practice of using import instead of require of called functions and reused variables - For example how should these require-lines look like as import?
const app = require('express')();
const server = require('http').createServer(app);
const io = require('socket.io')(server);
One possible way is to import the required functions and modules and use them in a next step:
import express from 'express';
import {createServer} from 'http';
import socketIo from 'socket.io';
const app = express();
const server = createServer(app);
const io = socketIo(server);
import and require both of them are good to use. But by convention in node almost use require over than import.
If you are very fond of ES6, then you can use import and other es6 features. But one thing should bear in mind that, when you are using es6, it is a good practice to bundle your code with bundeller (like webpack,babel)
I have main file called main.ts where I imported express with
import express from 'express';
Then I have another class in separate file where I want to create method "init" which has one parameter named "app" of type Express. But somehow i can't say app:Express without importing express.
My goal is to import express only once and keep it in a main.ts file, and then in a main.ts file I will call "init" method ( from a separate file) where I will pass that imported express.
Main.ts file
import express from 'express';
import { FriendsRouter } from './routes/friends.router';
const app = express();
FriendsRouter.init(app);
const PORT:number = 3000;
app.listen(PORT,()=>{
console.log('Listening at '+PORT);
})
Spearete file (friends router in my case)
export class FriendsRouter {
private constructor(){
}
public static init(app:Express): void{
app.get('/friends',someMethod);
}
}
Problem is, in FriendsRouter file, I can't say app: Express.
How can I fix this ?
The usual thing is to import the type Express from the express package:
import { Express } from "express";
Note that that's just importing the type, not the function. The rest of your code is then fine as-is (including the type on app).
If you don't have that type, install the types for express like this:
npm install --save-dev #types/express
...but you've probably already done that.
I have 2 require('express) calls.
First:
const express = require('express');
const app = express();
Second:
const Router = require('express');
const router = new Router();
What is the difference, why in the first we call a function, and in the second we create an object, if the methods are the same in both (use, get, post, etc)?
I think your question missed something. Your second example shows this:
const Router = require('express');
... but I think you meant to do this:
const Router = require('express').Router;
... regardless, the following should help you better understand.
In express, you can think of Routers as little mini applications... lightweight express apps... which have their own routing. In fact, the main "express" object is itself a Router. For example, you might have a bunch of endpoints for managing users:
// ./routes/user-routes.js
const userRoutes = new express.Router();
userRoutes.get('/', getAllUsers);
userRoutes.get('/:userId', getUserById);
userRoutes.post('/', createUser);
userRoutes.put('/:id', updateUser);
userRoutes.delete('/:id', removeUser);
Notice how none of the urls have anything like /users/ inside them. This is important because this little mini app can now be "mounted" (for lack of better terms) in a larger express app like follows:
const express = require('espress');
const userRoutes = require('./routes/user-routes');
const app = express();
app.use('/path/to/users', userRoutes);
Notice how the userRoutes were "mounted" on the /path/to/users such that all user requests will happen to the following URLs:
GET /path/to/users - get all users
GET /path/to/users/1234 - get user with id "1234"
... you get the point
This is mostly a convenient way to think about your app as a bunch of smaller mini apps which are orchestrated together.
Your second call is incorrect, you are just calling (requiring) express which is similar to your first call.
I never did const router = new Router();, so I'm not sure what that accomplish.
I generally do-
const router = require('express').Router();
router.get();
Even though with your first call you can do
app.get() and app.post()
According to express explanation
express.Router class is used to create modular, mountable route handlers. A Router instance is a complete middleware and routing system
Read more about it here
GeekforGeeks explains express.Router() very well
I would like to use require in a node/express app with typescript to import a json. I tried it like this:
const url = `./data/${resource}.json`;
const data = require(url);
but I get the error Cannot find module './data/my-data.json'.
I'd like to use require instead of an import in order to create the data variable dynamically depending on the value of the resource variable.
const path = require('path');
const url = path.resolve(__dirname, `./data/${resource}.json`);
const data = require(url);
The require keyword is a special keyword in nodejs. It is used to load modules, and since your json file is not a module, hence the error. Try this, this way you can dynamically load your json.
import fs from 'fs';
const file = fs.readFileSync(`./data/${resource}.json`).toString();
const data = JSON.parse(file);
There may be better ways to write this function, read mode about the fs module here.
Edit: As someone had alredy pointed out, it is actually possible to dynamicallyrequire json file. Here's how,
import path from 'path';
const uri = path.resolve(__dirname, `<path_to_json_file>`);
const data = require(uri);
However, as a standard practice, use the fs module to load static assets to your project.
import fs from 'fs';
const file = fs.readFileSync(`./data/${resource}.json`).toString();
const data = JSON.parse(file);
I have two files, one of them is the app.js and the otherone is api.js.
In the first file I have :
app.use(setHeader)
app.use(api.routes())
app.use(api.allowedMethods())
And in api.js I have:
import KoaRouter from 'koa-router';
const api = new Router();
//Validatekey
const validateKey = async (ctx, next) => {
const { authorization } = ctx.request.headers;
console.log(authorization);
if (authorization !== ctx.state.authorizationHeader) {
return ctx.throw(401);
}
await next();
}
api.get('/pets', validateKey, pets.list);
When I run the project a error message is throw: Router is not defined.
But If I write both files together, the application go fine.
Anybody knows the problem?
I have solved with var Router = require('koa-router')
The import is currently not implemented in nodejs, neither is it supported in the latest ES2015(ES6).
You will need to use a transpiler like Babel to use import in code.I advice that avoid transpiler as it cause performance issues on production just go with require and it will work.
Obviously Nodejs does not support import / export syntax and using require will solve your problem.
However it is possible to make import work on Node.js by using babel transformers.
Look the following answer for more information https://stackoverflow.com/a/37601577/972240