in package/src/languageServiceManager/kustoLanguageService.ts [1999:2010]
private insertToString(originalString: string, stringToInsert: string, offsetFromEnd: number): string {
let index = originalString.length + offsetFromEnd;
if (offsetFromEnd >= 0 || index < 0) {
return originalString; // Cannot insert before or after the string
}
let before = originalString.substring(0, index);
let after = originalString.substring(index);
return before + stringToInsert + after;
}