Upload a File in JavaScript – onlinecode

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2 years ago

Upload a File in JavaScript – onlinecode

In this post, we will give you information about Upload a File in JavaScript – onlinecode. Here we will give you detail about Upload a File in JavaScript – onlinecode And how to use it also give you a demo for it if it is necessary.

HTML has a file input tag that lets users select one or more files to upload. For example, below is HTML that defines a file input.

<input type="file" />

Given an <input type="File">, you can access the selected file as a blob by accessing
input.files[0]:

const input = document.querySelector('input[type="file"]');
const file = input.files[0];

file instanceof File; // true
file instanceof Blob; // true

Uploading a File

Once you have a blob, you can upload it using JavaScript’s built-in FormData class. Axios supports HTTP POST requests with FormData, so uploading a file is easy:

const formData = new FormData();
formData.append('myimage.png', file);

// Post the form, just make sure to set the 'Content-Type' header
const res = await axios.post('/upload', formData, {
  headers: {
    'Content-Type': 'multipart/form-data'
  }
});

Server-Side Setup

Parsing FormData uploads on the server side is tricky, you should use an npm module like Formidable to help you out. Below is how you can write the corresponding POST /upload endpoint to the above Axios
request.

Note that the below code just returns the file name, it doesn’t actually store the file. Once you have the parsed file
in Node.js, you would need to either upload the file to AWS S3 or some other storage service, or
store it on your server’s hard drive using fs.

app.post('/upload', function(req, res) {
  const form = new formidable.IncomingForm();
  // Parse 'req' and upload all associated files
  form.parse(req, function(err, fields, files) {
    if (err) {
      return res.status(400).json({ error: err.message });
    }
    const [firstFileName] = Object.keys(files);

    res.json({ filename: firstFileName });
  });
});

For example, here’s an upload endpoint that uploads the file to a bucket named ‘onlinecode-test’ in AWS S3:

const AWS = require('aws-sdk');

app.post('/upload', function(req, res) {
  const form = new formidable.IncomingForm();
  // Parse 'req' and upload all associated files
  form.parse(req, function(err, fields, files) {
    if (err) {
      return res.status(400).json({ error: err.message });
    }

    const [firstKey] = Object.keys(files);
    const upload = {
      Bucket: 'onlinecode-test',
      Body: fs.createReadStream(files[firstKey].path),
      Key: files[firstKey].name
    };
    s3.upload(upload, (err) => {
      if (err) {
        return res.status(400).json({ error: err.message });
      }
      return res.json({ ok: 1 });
    });
  });
});

JavaScript Fundamentals

JavaScript is a programming language that is used to create interactive web pages. It is a client-side scripting language, which means that it runs on the user’s browser. JavaScript can be used to add animation, interactivity, and functionality to web pages.

Here are some of the fundamentals of JavaScript:

Variables: Variables are used to store data. They are declared using the var keyword.
Data types: JavaScript has a variety of data types, including strings, numbers, booleans, objects, and arrays.
Operators: Operators are used to perform operations on data.
Control flow statements: Control flow statements allow you to control the order in which your code is executed.
Functions: Functions are blocks of code that can be reused.
Objects: Objects are used to store data in key-value pairs.
Arrays: Arrays are used to store data in a sequential order.
Events and event handlers: Events are notifications that are sent by the browser when something happens, such as when the user clicks on an element or moves the mouse over an element. Event handlers are functions that are called in response to an event.
DOM manipulation: The Document Object Model (DOM) is a tree-like structure that represents the elements of a web page. JavaScript can be used to manipulate the DOM to change the appearance or behavior of a web page.

These are just some of the fundamentals of JavaScript. There are many other concepts that you can learn as you continue to develop your skills.

Here are some resources that you can use to learn more about JavaScript:

Mozilla Developer Network (MDN): The MDN is a great resource for learning about JavaScript. It has a comprehensive reference guide, tutorials, and articles on a wide range of topics.
W3Schools: W3Schools is another great resource for learning about JavaScript. It has interactive tutorials and quizzes that can help you learn the basics of the language.
JavaScript.info: JavaScript.info is a website that provides in-depth tutorials on JavaScript. It also has a forum where you can ask questions and get help from other JavaScript developers.