Transform an SVG into a data URI—best practice

README.md

How to transform an SVG into a data URI

by Jenny Knuth, based on the work of Chris Coyier and Taylor Hunt

A data URI is a nice way to include a web resource without needing to make an HTTP request. Chris Coyier explains the technique nicely in Probably Don't Base64 SVG.

While a PNG might use Base64 encoding, for SVG, there is a better way.

Taylor Hunt's experiments led to this solution for optimizing SVGs in data URIs:

"So the best way of encoding SVG in a data URI is data:image/svg+xml,[actual data]. We don’t need the ;charset=utf-8 parameter (or the invalid ;utf8 parameter…), because URLs are always ASCII."

Here is a step-by-step method to create your encoded SVG string to include as a data URI:

1. Run your SVG file through svgo to optimize. (Directions are found at the svgo link.)

2. In your text editor, replace all double quotes in your SVG file with single quotes. Make sure there are no line breaks.

3. Replace all non-ASCII and URL-unsafe characters by running your SVG string through an encoding function like the one below by Taylor Hunt—surround your svgString with double quotes in the function's argument.

4. Paste your encoded SVG into your HTML tag's src attribute or CSS's url call using double quotes, after the data:image/sg+xml, prefix.

Examples:

HTML:

<img src="data:image/svg+xml,%3Csvg width='247' height='34' xmlns='http://www.w3.org/2000/svg'%3E%3Cg fill='none' fill-rule='evenodd'%3E%3Cg fill='%23FFF' fill-rule='non.zero'%3E%3Cpath d='M13.918 ... 4.022-2.888 4.57V26h-4.46V7.975z' fill='%23D7DCE1'/%3E%3C/g%3E%3C/svg%3E"/>

CSS:

.logo {
  background: url("data:image/svg+xml,%3Csvg ... /svg%3E");
}

The %3svg starts your encoded string and the svg%3E ends your encoded string.

Let me know if any questions.

encodeSvg.js

// this function is from the work of Taylor Hunt found at https://codepen.io/tigt/post/optimizing-svgs-in-data-uris

function encodeSvg(svgString) {
  return svgString.replace('<svg',(~svgString.indexOf('xmlns')?'<svg':'<svg xmlns="http://www.w3.org/2000/svg"'))
        
        //
        //   Encode (may need a few extra replacements)
        //
        .replace(/"/g, '\'')
        .replace(/%/g, '%25')
        .replace(/#/g, '%23')       
        .replace(/{/g, '%7B')
        .replace(/}/g, '%7D')         
        .replace(/</g, '%3C')
        .replace(/>/g, '%3E')

        .replace(/\s+/g,' ') 
        // 
        //    The maybe list (add on documented fail)
        // 
        //  .replace(/&/g, '%26')
        //  .replace('|', '%7C')
        //  .replace('[', '%5B')
        //  .replace(']', '%5D')
        //  .replace('^', '%5E')
        //  .replace('`', '%60')
        //  .replace(';', '%3B')
        //  .replace('?', '%3F')
        //  .replace(':', '%3A')
        //  .replace('@', '%40')
        //  .replace('=', '%3D')
  ;}