Get file size, image width and height before upload

web-development

file-reader-api

image-validation

responsive-design

byNikita Barsukov·Dec 5, 2024

document.getElementById('fileInput').onchange = (e) => {
  const [file] = e.target.files; // One solitary file. 🧐
  const reader = new FileReader(); // Our trusty file reader. 📖
  reader.onload = ({ target }) => {
    const img = new Image(); // Time for art! 🖼
    img.onload = () => alert(`Size: ${file.size} bytes, Width: ${img.width}px, Height: ${img.height}px`); // Tada! 🎉
    img.src = target.result;
  }
  reader.readAsDataURL(file); // Decode that Base64! 🧪
};

This FileReader implementation will give you all the juicy details about your file, specifically the dimensions and file size.

Improving previews with File and URL APIs

You want to ensure users get immediate feedback in regard to their uploaded images. This improves the overall user experience. Here’s a tip: clear any previous previews after they have fulfilled their purpose. URL.revokeObjectURL is your friend here, helping manage memory by clearing the cached data.

When handling multiple file uploads, remember they are like snowflakes: each one is unique. So, iterate and validate each file separately. Unsupported file formats? Inform the user and let them know their snowflake...ahem, I mean file, isn’t compatible with your site. But be mindful of browser compatibility, to ensure your site functions uniformly across all modern browsers.

Advanced validation techniques with FileReader and jQuery

Validation plays a pivotal role in seamless user experience. Fancy up your validation by using HTML5 canvas to resize images while maintaining aspect ratio. If you want to make the validation process smooth as butter, consider the jQuery's validation plugin.

By utilizing FileReader.readAsDataURL, you can maintain a seamless user flow by displaying Base64 encoded image previews. And, with the Image.onload, you can get the image width and height. Oh, and don't be shy to check on jsFiddle or CodePen for hands-on examples!

Mindful handling of mobile limitations

Mobile devices invariably present unique rules for file handling and UI experience. Testing thoroughly on various devices safeguards a consistent UX across platforms. Be mindful that FileReader API might behave a bit different on mobile devices.

Practical implementation and potential challenges

File size and dimension checks are an essential element in different applications. E.g., an e-commerce platform may need a specific resolution of images or a social networking site might have a limit on file size.

Testing across different file types is a must to guarantee a healthy range of functionality. Equipping your website with a strong validation can ensure the right file specifications.

Remember, immediacy of feedback to users plays a big role in maintaining an optimized experience. It's always better to guide the user to upload the correct file rather than feeding them with error messages.

Now, for the cherry on top: keep asynchronous nature of the FileReader API in mind for managing performance of the application.

explain-codes / Web development / Get file size, image width and height before upload

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