I recently had a few global variables that I was referencing from a TypeScript file that TypeScript marked with the following error:

Property 'msSpeechRecognition' does not exist on type 'Window & typeof globalThis'.

So I created added the following code into my env.d.ts (generated and referenced in tsconfig.json by create-vue):

declare const msSpeechRecognition: undefined | SpeechRecognitionStatic;

This didn't fix the problem. However, when I switched the code to the following:

declare var msSpeechRecognition: undefined | SpeechRecognitionStatic;

The error on the reference to msSpeechRecognition disappeared. I understand the differences between const and var in JavaScript, but what are the differences when using them in type declarations?

I couldn't reproduce this same issue when replacing SpeechRecognitionStatic with string, so I know it's something related to the SpeechRecognitionStatic type. Here is how it looked like (brought from @types/webspeechapi):

interface SpeechRecognitionStatic {
    prototype: SpeechRecognition;
    new (): SpeechRecognition;
}