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data:
URLsThis package helps you parse data:
URLs according to the WHATWG Fetch Standard:
const parseDataURL = require("data-url");
const textExample = parseDataURL("data:,Hello%2C%20World!");
console.log(textExample.mimeType.toString()); // "text/plain;charset=US-ASCII"
console.log(textExample.body.toString()); // "Hello, World!"
const htmlExample = dataURL("data:text/html,%3Ch1%3EHello%2C%20World!%3C%2Fh1%3E");
console.log(htmlExample.mimeType.toString()); // "text/html"
console.log(htmlExample.body.toString()); // <h1>Hello, World!</h1>
const pngExample = parseDataURL("data:image/png;base64,iVBORw0KGgoAAA" +
"ANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4" +
"//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU" +
"5ErkJggg==");
console.log(pngExample.mimeType.toString()); // "image/png"
console.log(pngExample.body); // <Buffer 89 50 4e 47 0d ... >
This package's main module's default export is a function that accepts a string and returns a { mimeType, body }
object, or null
if the result cannot be parsed as a data:
URL.
mimeType
property is an instance of whatwg-mimetype's MIMEType
class.body
property is a Node.js Buffer
instance.As shown in the examples above, both of these have useful toString()
methods for manipulating them as string values. However…
Because Node.js's Buffer.prototype.toString()
assumes a UTF-8 encoding, simply doing dataURL.body.toString()
may not work correctly if the data:
URL's contents were not originally written in UTF-8. This includes if the encoding is "US-ASCII", aka windows-1252, which is notable for being the default in many cases.
A more complete decoding example would use the whatwg-encoding package as follows:
const parseDataURL = require("data-url");
const { labelToName, decode } = require("whatwg-encoding");
const dataURL = parseDataURL(arbitraryString);
const encodingName = labelToName(dataURL.mimeType.parameters.get("charset"));
const bodyDecoded = decode(dataURL.body, encodingName);
For example, given an arbitraryString
of data:,Hello!
, this will produce a bodyDecoded
of "Hello!"
, as expected. But given an arbitraryString
of "data:,Héllo!"
, this will correctly produce a bodyDecoded
of "Héllo!"
, whereas just doing dataURL.body.toString()
will give back "Héllo!"
.
In summary, only use dataURL.body.toString()
when you are very certain your data is inside the ASCII range (i.e. code points within the range U+0000 to U+007F).
If you are using the whatwg-url package, you may already have a "URL record" object on hand, as produced by that package's parseURL
export. In that case, you can use this package's fromURLRecord
export to save a bit of work:
const { parseURL } = require("whatwg-url");
const dataURLFromURLRecord = require("data-url").fromURLRecord;
const urlRecord = parseURL("data:,Hello%2C%20World!");
const dataURL = dataURLFromURLRecord(urlRecord);
In practice, we expect this functionality only to be used by consumers like jsdom, which are using these packages at a very low level.