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  Understand JavaScript prototype

For an front end programming language like JavaScript, if we want to understand its OOP feature, we need to understand its objects, prototype chain, execution context, closure and this keyword in deep. If you have a good understanding on these concepts, you should be confident that you can handle this language well. The inheritance in JavaScript is not class inheritance like Java, but it adopts another mechanism-- prototype inheritance. The key to prototype inheritance is the prototype chain mec...

   JavaScript, prototype, __proto__     2013-02-02 02:34:09

  Some measures for improving Linux server security

The hackers often exploit server weakness to gain access control to some servers. With a scanner, aimlessly looking undefended host, backdoor, control, and sold to people in need. Some basic security measures can be taken on Linux servers to avoid being attacked by hackers. Disable root remote login As the default administrative account, root is the account which is most likely to be attacked.Disabling ssh remote login is necessary. Method: Edit / etc / ssh / sshd_config PermitRootLogin no At t...

   Linux server,Server security     2012-08-21 05:08:50

  Convert ext3 to ext4 file system on CentOS

ext3 is a journaled file system that is commonly used by the Linux kernel. It is the default file system for many popular Linux distributions, including Debian. Stephen Tweedie. On June 28, 2006, Theodore Ts'o, the principal developer of ext3, announced an enhanced version, called ext4. Today, we will show how to convert ext3 to ext4 format on CentOS. System environment: Release version : CentOS release 5.4(Final) Kernel:  Linux localhost.lo...

   CentOS, ext3 to ext4     2012-11-21 11:40:45

  Remove browse button from input type=file

In Web 2.0 era, many websites will ask the user to upload their avatar when creating their profile. In HTML, the input control we should use is input="file". This is a file control provided by the browser vendor and it should be ran in a sandbox for security consideration. Browsers don't provide ways to choose file from local and upload to the remote server without the input="file" control.  There is one annoying part about the input="file", which is a default button named "Choose File" or...

   file,html,browse,remove browse button     2015-07-12 05:17:51

  The tips of learning Linux kernel

  As the Linux kernel has become one of the most gigantic and complex software project in the world, its complication scare many novices away. In this post, I will give some personal experience on how to learn Linux kernel, and hope these tips can offer some help to newcomers. (1) Download vanilla kernel and install it. Yes, I suggest you can find a physical machine, or if you really don’t have one at hand, virtual machine is also OK. Download the newest vanilla k...

       2017-07-28 22:53:11

  MySQL index optimization

Problem description: We need to access a very big table which has 40 million records. In the table, id is the primary key and program_id is indexed. When executing a select query: select * from program_access_log where program_id between 1 and 4000 The above query executes very slowly, we thought it was because there were too many records in the table. So we added id in the where condition to limit the search so that each time only half a million records would be read. select * fr...

   MySQL,Index search, Partition     2012-12-26 13:14:20

  Create cron job on CentOS

These two days, I am building a website and deploying it on a VPS server which uses CentOS 5. I don't have cPanel or Plesk for my account, so I need to install and configure everything myself including Apache, PHP, MySQL and FTP server, also today's topic cron job. Since my website has a ranking algorithm to calculate the rankings of each link and update the ranking on database and I need to calculate the rankings every 5 minutes, so I think to use cron jobs. Here are what I have done which may ...

   cron job,crontab,CentOS,linux,php,example     2012-06-11 09:23:45

  Integer overflow

You may be familiar with integer overflow, but what you may not be familiar with is how gcc handles signed integer overflow. First let's look at the standard, for unsigned integer, the standard says : A computation involving unsigned operands can never overflow, because a result that cannot be represented by the resulting unsigned integer type is reduced modulo the number that is one greater than the largest value that can be represented by the resulting type. In other words, unsigned integer ov...

   Integer overflow,gcc,Linux     2012-10-20 13:33:10

  Select top 3 values from each group in a table with SQL

Yesterday, my friend Liu Bing asked me a question about how to select top 3 values for each person in a database table using SQL. I think this question is interesting and it deserves some thoughts. Here I record down how to solve this issue. Assume we have a table which has two columns, one column contains the names of some people and the other column contains some values related to each person. One person can have more than one value. Each value has a numeric type. The question is we want to se...

   SQL,Correlated query,top 3     2013-05-23 03:21:25

  Why localStorage only allows to store string values

localStorage allows data to be stored in browsers across sessions, the data will be there even though the session is expired. It is frequently used to store static data so that they can be loaded when needed. But as per spec, it says that the keys and the values are always strings (note that, as with objects, integer keys will be automatically converted to strings). Why cannot store the object as it is? Take a look at an example: var str = "test"; localStorage.setItem("str", str); cons...

   JAVASCRIPT,LOCALSTORAGE     2020-04-05 00:54:29

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