How Can I Preview Images Before Upload Using HTML5?

Previewing an Image Before Upload

In web development, it can be beneficial to provide users with a preview of an image before they submit it. This allows users to ensure the image is correct before uploading it, potentially reducing the number of errors and rework.

The Solution: HTML5 File Interface

Fortunately, the HTML5 File interface provides a simple way to preview images in the browser without making a server request or using Ajax. Here's how it works:

1. Create an Image Element

Create an HTML element with an id (e.g., blah) to display the image preview.

2. Get the File from the Input

Add an onchange event handler to the file input element. When a file is selected, the event handler extracts the selected file from the input element.

3. Use the File Interface

Create an object URL for the selected file using the URL.createObjectURL() method. This creates a temporary URL that allows the browser to display the image.

4. Update the Image Source

Set the src attribute of the element to the object URL. This will display the preview of the selected image.

Example Code

<input accept="image/*" type='file'>

imgInp.onchange = evt => {
  const [file] = imgInp.files;
  if (file) {
    blah.src = URL.createObjectURL(file);
  }
};

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