Encode a file to Base64-encoded string from file internal id using SuiteScript.

const encodeBase64 = (internalId) => {
            try {
                let fileObj = file.load({
                    id: internalId
                });
                return fileObj.getContents();
            } catch (error) {
                log.error('error@encodeBase64', error)
            }
        }