如何使用 JavaScript 上傳檔案？

How to Upload a File Using JavaScript

To upload a file using JavaScript, you can leverage the following steps:

1. Use Form Data:

   • Create a FormData object to store the file and additional data.
   • Append the file to the form data using formData.append() .

2. Make an XHR Request:

   • Create an XMLHttpRequest (XHR) object.
   • Set the request method to "POST" and the URL to the upload endpoint.
   • Set the body property of the XHR object to the formData .

3. Listen for Upload Events:

   • Add event listeners to the XHR object for the load , progress , and error events.
   • In these event handlers, you can handle the upload status and response.

Example Code:

const formData = new FormData();
const fileInput = document.getElementById('image-file');
const file = fileInput.files[0];

formData.append('photo', file);

const xhr = new XMLHttpRequest();
xhr.open('POST', '/upload/image');
xhr.send(formData);

xhr.addEventListener('load', () => {
  // Handle successful upload
});

xhr.addEventListener('progress', (e) => {
  // Monitor upload progress
});

xhr.addEventListener('error', (e) => {
  // Handle upload errors
});

Pure JavaScript:

If you want to use pure JavaScript without XHR, you can use the fetch API with FormData .

Example:

let photo = document.getElementById("image-file").files[0];
let formData = new FormData();

formData.append("photo", photo);
fetch('/upload/image', { method: "POST", body: formData });

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