Convert ascii to character?

This is really simple, but I can’t it after spending 20+ minutes searching on google! I just want a function that turns a number into a character; basically the inverse of mystring.charCodeAt(0). For example-

mytextfield.text = "a";
myasciinumber = mytextfield.charCodeAt(0); // 97
trace(theFunctionICantFind(myasciinumber)); // would trace an 'a'

If anyone can tell me what that is I’d appreciate it, thanks!