Go Home At Five

List of most common small mistakes that take a lot of time to debug and prevents developers to go home at 5PM.

• Sending AJAX Post Request
  JSON.stringify() if you are sending JSON.

• 0 means False when evaluated as a Boolean.

  if hashmap[key]:
      do something
  else:
      do something else
  

  Here, if the value is 0, the above if condition will return false, even when there is an element in the hashmap with the given key.

• Avoid using : character in id attribute of a HTML div element.
  As a purely practical matter, you may want to avoid certain characters. Periods, colons and '#' have special meaning in CSS selectors, so you will have to escape those characters using a backslash in CSS or a double backslash in a selector string passed to jQuery. Think about how often you will have to escape a character in your stylesheets or code before you go crazy with periods and colons in ids.

  For example, the HTML declaration <div id="first.name"></div> is valid. You can select that element in CSS as #first\.name and in jQuery like so: $('#first\\.name'). But if you forget the backslash, $('#first.name'), you will have a perfectly valid selector looking for an element with id first and also having class name. This is a bug that is easy to overlook. You might be happier in the long run choosing the id first-name (a hyphen rather than a period), instead. Source

• Python - Using mutable default value (list, dict etc) for function arguments.
  This can lead to trippy behavior explained at https://stackoverflow.com/questions/1132941/least-astonishment-and-the-mutable-default-argument which further directs to http://effbot.org/zone/default-values.htm . TLDR- functions are first class objects in python.

• Java - parseBoolean VS getBoolean [TODO]