How to Read File Uploads in JavaScript

Publié le: 06 juin 2024
sur la chaîne: Dev Kylo & The Great Sync

Usually when you upload a file in an form, you would send that file directly to the server. But did you know you can access that file in the BROWSER.

I’m not just talking about the file properties, like its size and type. I mean the actual contents of the file!

Using the FileReader API is like many other browser APIS - there’s a constructor function, which we use to create an instance.

Once we have the instance, we can access a bunch of different methods to use for reading files, such as:

`readAsText(file)`: Reads the file as text.
`readAsDataURL(file)`: Reads the file and encodes it as a base64 data URL.
`readAsArrayBuffer(file)`: Reads the file into an ArrayBuffer.
`readAsBinaryString(file)`: Reads the file as a binary string.

In my example, I’m using the`readAsText(file)` to read the contents of a text file and display it on the webpage.

Key Points:

We handle the file upload event using the `onChange` attribute on the input element.
We create a new `FileReader` instance to read the uploaded file.
We check the file type to ensure only text files are processed.
We read the file content and display it in the designated div.

Checkout thegreatsync.com for my free short course on a Visual Deep Dive into Objects.

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