How to upload a file using Fetch
How to upload files to the server using the Fetch API, explained in a simple way
There’s a task that should be simple, but sometimes it leads to hours of research on the Web: uploading files to the server.
In this tutorial I explain you how to do so using fetch
.
Given a form with a file input field:
<input type="file" id="fileUpload" />
We attach a change
event handler on it:
document.querySelector('#fileUpload').addEventListener('change', event => {
handleImageUpload(event)
})
and we manage the bulk of our logic in the handleImageUpload()
function:
const handleImageUpload = event => {
const files = event.target.files
const formData = new FormData()
formData.append('myFile', files[0])
fetch('/saveImage', {
method: 'POST',
body: formData
})
.then(response => response.json())
.then(data => {
console.log(data)
})
.catch(error => {
console.error(error)
})
}
In this example we POST to the /saveImage
endpoint.
We initialize a new FormData
object and we assign it to the formData
variable, and we append there the uploaded file. If we have more than one file input element, we’d have more than one append()
call.
The data
variable inside the second then()
will contain the JSON parsed return data. I’m assuming your server will give you JSON as a response.
See how to handle images uploaded server-side
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