Read Local Files in JavaScript with FileReader – onlinecode

Read Local Files in JavaScript with FileReader

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

JavaScript’s FileReader is a class that enables you to read a file on the user’s
machine from JavaScript running in the browser. FileReader is typically
used to read data from an <input type="file">.

For example, suppose you have a file input on your page with id select-file.
Here’s how you can print out the contents of the currently selected file.

const file = document.querySelector('#select-file').files[0];
const reader = new FileReader();

reader.onload = res => {
  console.log(; // Print file contents
reader.onerror = err => console.log(err);


Below is a live example that prints file contents to the console
every time you select a different file. Click Ctrl+Shift+J on Linux/Windows
or Cmd+J on OSX to open up the Chrome console and try it out!

FileReader is well supported in modern browsers, as well as IE10.
Note that FileReader is a browser API, so, while most browsers
support it, FileReader is not part of Node.js.

With Promises and Async/Await

The FileReader class’ async API isn’t ideal for usage with async/await or promise chaining. Here’s how you can wrap a FileReader
in a promise for chaining:

function readFile(file) {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();

    reader.onload = res => {
    reader.onerror = err => reject(err);


With the above readFile() helper, you can read a file in an async

async function onSubmit() {
  const file = document.querySelector('#select-file').files[0];

  const contents = await readFile(file);


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.
  • 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.

I hope this helps!

Here are some additional tips for learning JavaScript:

  • Start with the basics: Before you start trying to build complex applications, it’s important to learn the basics of JavaScript. This includes things like variables, data types, operators, and control flow statements.
  • Practice regularly: The best way to learn JavaScript is to practice regularly. Try to find some time each day to work on JavaScript projects.
  • Get help from others: If you get stuck, don’t be afraid to ask for help from others. There are many online forums and communities where you can get help from other JavaScript developers.

With a little practice, you’ll be able to learn JavaScript and start building amazing web applications.

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