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26. September 2013

jQuery: check whether an element exists

Filed under: JavaScript — Tags: , , , — Christopher Kramer @ 13:47

In traditional JavaScript, to check if some element exists, you’d have done something like this:


Of course this still works but what about using JQuery? So you might try this:


But this will always be true as jQuery always returns an object, no matter whether the selector matched or not.So what you can do is the following:

if($('#someID').length > 0)

This will do the trick. You can even leave out “> 0”:


The cool thing is you can use this also to check more complex stuff, like whether #someID has an <img> child-element:

if($('#someID img').length)

And this is where jQuery really makes life a lot easier because with traditional JavaScript, this would be a bit lengthy for what it does.

Have fun!


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1. September 2013

MySQL: reset a forgotten MySQL root password

Filed under: DBMS,Linux,Security,Server Administration — Christopher Kramer @ 14:37

Just in case you don’t know the password of your MySQL root user anylonger, this is how you can set a new one.

Windows users, follow this guide.

Linux / Unix users: This is for Debian (wheezy) and MySQL 5.5, but should work more or less the same on any linux/unix:

Either do this as (linux user) root or prefix every command with sudo:

  1. Stop the MySQL server
    service mysql stop
  2. Create a init file:
    touch /etc/mysql/mysql-init
  3. Write the following into this file (adjust the PW):
    SET PASSWORD FOR 'root'@'localhost' = PASSWORD('MyNewPassword');
  4. Restart MySQL with this init-file:
    mysqld_safe --init-file=/etc/mysql/mysql-init
  5. The new password should work now. Try it:
    mysql -u root -p
  6. Restart MySQL normally:
    service mysql restart
  7. Remove the init-file
    rm /etc/mysql/mysql-init

And you’re done. I hope this helps somebody.

Note: if it does not work, it is most likely because the MySQL process cannot access the init-file (e.g. because of missing access rights). In this case check your (sys)logs for stuff like this:

mysqld: 130901 14:20:30 [ERROR] /usr/sbin/mysqld: File '/root/mysql-init' not found (Errcode: 13)

I had this problem first because I tried creating the init-file in /root where the mysql-process was not able to read it.