NSString *content = @"哈哈哈哈test哈t123哈哈哈哈";
    
NSLog(@"替换前--- %@",content);

NSRegularExpression *regularExpression = [NSRegularExpression regularExpressionWithPattern:@"[a-zA-Z0-9]" options:0 error:nil];
content = [regularExpression stringByReplacingMatchesInString:content options:0 range:NSMakeRange(0, content.length) withTemplate:@"*"];

NSLog(@"替换后--- %@",content);

var str = '123你好呀hehe';
console.log(str.replace(/\w|\d/gi, '*'))

这样不行吗?

var str = '123你好呀hehe';
console.log(str.replace(/\w/g, '*'));

循环一遍，直接对ASCII码进行判断不就行了吗，用c的语法做，一个一个字符对比并更改