由字母、数字、特殊字符,任意2种组成,8-20位
/^(?![a-zA-Z]+$)(?!\d+$)(?![^\da-zA-Z\s]+$).{8,20}$/ js测试 /^(?![a-zA-Z]+$)(?!\d+$)(?![^\da-zA-Z\s]+$).{8,20}$/.test('12345678!$a')