Category: JavaScript

To fix await not waiting for promise with JavaScript async function, we use await on a promise.

For instance, we write

const func = async () => console.log(await getResult());

to call getResult to return a promise.

And then we use await to get the resolve value of the returned promise.

To set request header when making connection with JavaScript socket.io-client, we set the extraHeaders property.

For instance, we write

const socket = io("http://localhost", {
  extraHeaders: {
    Authorization: "Bearer authorization_token_here",
  },
});

to set extraHeaders to an object with the header keys-value pairs.

To get Node.js Express to listen only on localhost, we call listen with the port only.

For instance, we write

app.listen(3001);

to only listen to port 3001 on localhost for requests.

To fix CORS error :Request header field Authorization is not allowed by Access-Control-Allow-Headers in preflight response with Node, we use the cors package.

To use it, we write

const express = require("express");
const cors = require("cors");
const app = express();
app.use(cors());
app.options("*", cors());

to call app.use with the middleware returned by cors to enable CORS in our Express app.

To fix this error TypeError [ERR_INVALID_CALLBACK]: Callback must be a function with Node, we pass in a function as the callback.

For instance, we write

const fs = require("fs");

fs.readFile("readMe.txt", "utf8", (err, data) => {
  fs.writeFile("writeMe.txt", data, (err, result) => {
    if (err) console.log("error", err);
  });
});

to call readFile with the callback as the 3rd argument.

And we call writeFile with the callback as the 3rd argument.