How to get Data URL synchronously?

Question

JavaScript

Using XMLHttpRequest I can synchronously download the file I need.
How would I then also synchronously convert the downloaded to Data URL ?

This is for a browser extension. The chrome.webRequest.onBeforeRequest event requires a synchronous callback as its first parameter. Allows you to edit the scripts of the target site. That is, inside this event, I can synchronously download the current script, make edits, and then send it back as a redirect to Data URL .

Answer 1

Download the file as an ArrayBuffer, then encode it as base64
, for example, this
btoa is a little crazy - be sure to give it an array of bytes as a string, that is, for example, a binary array [208, 144, 208, 145], which symbolizes the string "AB" in the encoding utf8 must be converted to a string of 4 characters String.fromCharCode(208, 144, 208, 145). But in principle it is also possible.
Well, btoa is not suitable for the downloaded string, because the text there is already in utf16