function prevChar(char : string) : string {
return String.fromCharCode(char.charCodeAt(0) - 1);
}
console.log(prevChar('a'));
console.log(prevChar('b'));
console.log(prevChar('c'));
console.log(prevChar('A'));
console.log(prevChar('B'));
console.log(prevChar('C'));
/*
run:
"`"
"a"
"b"
"@"
"A"
"B"
*/