How to open one or multiple files

Dealing with files is one of the most common operations for apps on the web. Traditionally, users needed to upload a file, make some changes to it, and then download it again, resulting in a copy in the Downloads folder. With the File System Access API, users can now open files directly, make modifications, and save back the changes to the original file.

The modern way

Using the File System Access API's showOpenFilePicker() method

To open a file, call showOpenFilePicker(), which returns a promise with an array of the picked file or files. If you need multiple files, you can pass { multiple: true, } to the method.

{% BrowserCompat 'api.Window.showOpenFilePicker' %}

The classic way

Using the <input type="file"> element

The <input type="file"> element on a page allows the user to click it and open one or multiple files. The trick now consists of inserting the element invisibly into a page with JavaScript and clicking it programmatically.

{% BrowserCompat 'html.elements.input' %}

Progressive enhancement

The method below uses the File System Access API when it's supported and else falls back to the classic approach. In both cases the function returns an array of files, but in case of where the File System Access API is supported, each file object also has a FileSystemFileHandle stored in the handle property, so you can optionally serialize the handle to disk.

const openFileOrFiles = async (multiple = false) => {
  // Feature detection. The API needs to be supported
  // and the app not run in an iframe.
  const supportsFileSystemAccess =
    "showOpenFilePicker" in window &&
    (() => {
      try {
        return window.self === window.top;
      } catch {
        return false;
      }
    })();
  // If the File System Access API is supported…
  if (supportsFileSystemAccess) {
    let fileOrFiles = undefined;
    try {
      // Show the file picker, optionally allowing multiple files.
      const handles = await showOpenFilePicker({ multiple });
      // Only one file is requested.
      if (!multiple) {
        // Add the `FileSystemFileHandle` as `.handle`.
        fileOrFiles = await handles[0].getFile();
        fileOrFiles.handle = handles[0];
      } else {
        fileOrFiles = await Promise.all(
          handles.map(async (handle) => {
            const file = await handle.getFile();
            // Add the `FileSystemFileHandle` as `.handle`.
            file.handle = handle;
            return file;
          })
        );
      }
    } catch (err) {
      // Fail silently if the user has simply canceled the dialog.
      if (err.name !== 'AbortError') {
        console.error(err.name, err.message);
      }
    }
    return fileOrFiles;
  }
  // Fallback if the File System Access API is not supported.
  return new Promise((resolve) => {
    // Append a new `<input type="file" multiple? />` and hide it.
    const input = document.createElement('input');
    input.style.display = 'none';
    input.type = 'file';
    document.body.append(input);
    if (multiple) {
      input.multiple = true;
    }
    // The `change` event fires when the user interacts with the dialog.
    input.addEventListener('change', () => {
      // Remove the `<input type="file" multiple? />` again from the DOM.
      input.remove();
      // If no files were selected, return.
      if (!input.files) {
        return;
      }
      // Return all files or just one file.
      resolve(multiple ? Array.from(input.files) : input.files[0]);
    });
    // Show the picker.
    if ('showPicker' in HTMLInputElement.prototype) {
      input.showPicker();
    } else {
      input.click();
    }
  });
};

Further reading

• File System Access API

Demo