How to encode a string to base 64 in the airtable javascript code editor?

I am trying to make an api request from the aritable script editor.
The GET request require an Authorization header that contains a Base64 digest of the authentication string api: USERNAME:YOUR_API_KEY.

It is not possible to use btoa() for encoding in airtable as it is not defined. I checked SO, and one solution to encode without using btoa was the following.

var Base64={_keyStr:"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",encode:function(e){var t="";var n,r,i,s,o,u,a;var f=0;e=Base64._utf8_encode(e);while(f<e.length){n=e.charCodeAt(f++);r=e.charCodeAt(f++);i=e.charCodeAt(f++);s=n>>2;o=(n&3)<<4|r>>4;u=(r&15)<<2|i>>6;a=i&63;if(isNaN(r)){u=a=64}else if(isNaN(i)){a=64}t=t+this._keyStr.charAt(s)+this._keyStr.charAt(o)+this._keyStr.charAt(u)+this._keyStr.charAt(a)}return t},decode:function(e){var t="";var n,r,i;var s,o,u,a;var f=0;e=e.replace(/[^A-Za-z0-9\+\/\=]/g,"");while(f<e.length){s=this._keyStr.indexOf(e.charAt(f++));o=this._keyStr.indexOf(e.charAt(f++));u=this._keyStr.indexOf(e.charAt(f++));a=this._keyStr.indexOf(e.charAt(f++));n=s<<2|o>>4;r=(o&15)<<4|u>>2;i=(u&3)<<6|a;t=t+String.fromCharCode(n);if(u!=64){t=t+String.fromCharCode(r)}if(a!=64){t=t+String.fromCharCode(i)}}t=Base64._utf8_decode(t);return t},_utf8_encode:function(e){e=e.replace(/\r\n/g,"\n");var t="";for(var n=0;n<e.length;n++){var r=e.charCodeAt(n);if(r<128){t+=String.fromCharCode(r)}else if(r>127&&r<2048){t+=String.fromCharCode(r>>6|192);t+=String.fromCharCode(r&63|128)}else{t+=String.fromCharCode(r>>12|224);t+=String.fromCharCode(r>>6&63|128);t+=String.fromCharCode(r&63|128)}}return t},_utf8_decode:function(e){var t="";var n=0;var r=c1=c2=0;while(n<e.length){r=e.charCodeAt(n);if(r<128){t+=String.fromCharCode(r);n++}else if(r>191&&r<224){c2=e.charCodeAt(n+1);t+=String.fromCharCode((r&31)<<6|c2&63);n+=2}else{c2=e.charCodeAt(n+1);c3=e.charCodeAt(n+2);t+=String.fromCharCode((r&15)<<12|(c2&63)<<6|c3&63);n+=3}}return t}}

const stringApi = 'USER_NAME:API_KEY'
var encodedString = Base64.encode(stringApi)

let response = await fetch('https://api.com', {
    method: 'GET',
    header: {
        'Authorization': 'Basic ' + encodedString 
    }
})

This however still fails to connect to the api as I keep getting 401 UNAUTHORIZED responses from the api.

I assumed perhaps this method of encoding was not correct, so I encoded the stringApi using btoa() in my local machine, and then copied the result of that encoding into the Authorization in the header. That also did not work as I kept getting 401 responses.

I am wondering if you know or have any suggestions on how to properly encode to base 64 using the airtable code editor so I can successfully connect to the server and stop getting 401 responses.

Thanks in advance!

This is frustrating on many levels. Enough so, that I have a dedicated 'scenario' using make.com to return a base64 of any input I send it...

    async function btoa(inputString){

    // Fetch from Make
    let apiResponse = await fetch(`https://hook.us1.make.com/wa0..r?s=${inputString}`);
    let data = await apiResponse.text();
    return data.toString()

    }

On the make.com side, there is the btoa function to apply to any input string.