Category: JavaScript Answers

To convert a Buffer into a ReadableStream in Node.js, we call the Readable.from method.

For instance, we write

const { Readable } = require("stream");

const stream = Readable.from(myBuffer);

to call Readable.from to convert the myBuffer to a readable stream.

This is avilable from Node.js 10.17.0 and up.

To write a .nvmrc file which automatically change Node version, we put the Node version into the file.

For instance, we we run

$ node -v > .nvmrc

to get the Node.js version with node -v and put it into the .nvmrc file with >.

To send file in response with Node.js, we call pipe to pipe a stream.

For instance, we write

const http = require("http");
const fileSystem = require("fs");
const path = require("path");

http
  .createServer((request, response) => {
    const filePath = path.join(__dirname, "myfile.mp3");
    const stat = fileSystem.statSync(filePath);

    response.writeHead(200, {
      "Content-Type": "audio/mpeg",
      "Content-Length": stat.size,
    });

    const readStream = fileSystem.createReadStream(filePath);
    readStream.pipe(response);
  })
  .listen(2000);

to call createServer with a callback that calls createReadStream to read the file at filePath.

Then we call readStream.pipe with response to pipe the file data as the response.

We call writeHead to write the file metadata as the header.

To fix npx command not found with JavaScript, we can install it.

To install it, we run

npm i -g npx

to install npx globally with npm i -g.

To upload base64 encoded Image to Amazon S3 via Node.js, we call the putObject method.

For instance, we write

const AWS = require("aws-sdk");
AWS.config.loadFromPath("./s3_config.json");
const s3Bucket = new AWS.S3({ params: { Bucket: "myBucket" } });
const buf = Buffer.from(
  req.body.imageBinary.replace(/^data:image\/\w+;base64,/, ""),
  "base64"
);
const data = {
  Key: req.body.userId,
  Body: buf,
  ContentEncoding: "base64",
  ContentType: "image/jpeg",
};
s3Bucket.putObject(data, (err, data) => {
  if (err) {
    console.log(err);
    console.log("Error uploading data: ", data);
  } else {
    console.log("successfully uploaded the image!");
  }
});

to convert the base64 string to a buffer with the Buffer.from method.

We replace the prefix with 'base64' before doing the conversion with replace.

Then we create a data object with Body set to the buf buffer.

Finally, we call putObject to upload the data.