Is it possible to retrieve the image file size from a data URI?
Consider an IMG element with the following src:
src="data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD...
Can the image file size be obtained using plain JavaScript based on the src without making a server request?
To determine the file size, you can decode the base64 string and then check its length.
var imageSrc ="data:image/jpeg;base64,R0lGODlhAQABAIAAAP///wAAACH5BAAAAAAALAAAAAABAAEAAAICRAEAOw==";
var data = imageSrc.substring(22);
var decodedData = atob(data);
console.log("File Size: " + decodedData.length);For a rough estimate, you can calculate that the file size is typically around 75% of the base64 string's size. The actual size would not exceed this estimate and could be up to two bytes smaller.
If you prefer a quick solution, you can simply use atob() and check the length as suggested in other responses.
However, for precise measurements with optimal performance (especially important for handling massive files or multiple files), consider factoring in padding when calculating the exact size:
let base64Length = src.length - (src.indexOf(',') + 1);
let padding = (src.charAt(src.length - 2) === '=') ? 2 : ((src.charAt(src.length - 1) === '=') ? 1 : 0);
let fileSize = base64Length * 0.75 - padding;
This method avoids parsing the entire string and should only be used if seeking extreme optimization or facing memory constraints.
To determine the size of a base64 string, calculate its length directly.
Understanding base64 string length
By converting the base64 string to a regular string with atob(), you can easily check its length to approximate the image's actual size. Remember, there is no need to include the data:image/jpeg;base64, prefix when checking the size.
This code snippet offers a versatile solution that can handle various types of base64 strings, utilizing the algorithm originally developed by Daniel Trans.
let source ="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP/// yH5BAEAAAAALAAAAAABAAEAAAIBRAA7";
let base64string = source.split('base64,')[1];
let decodedString = atob(base64string);
console.log("Final Size: " + decodedString.length);
Instead of relying on the deprecated atob method, this solution showcases how to achieve the same result using Buffer in a modern way.
const imgSrc="data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD...";
const base64String = imgSrc.split('base64,')[1]; //extract image data
const imageData = Buffer.from(base64String, 'base64'); //encode image as bytes
console.log('Image Size: ' + imageData.length);
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