Reasons why id based selectors don't work

1. element/DOM with id specified doesn't exist yet.
2. element exist but is not registered in DOM [in case of HTML nodes appended dynamically from ajax responses]
3. more than one elements with same id are present which is causing conflict.

solutions

1. try to access element after its declaration or alternatively use stuff like $(document).ready();

2. for elements coming from ajax responses, use .bind() method of jquery, older versions of jquery had .live() for the same.

3. use tools [eg webdeveloper plugin for browsers] to find duplicate ids and remove them.

Reasons why id based selectors don't work

1. The element/DOM with id specified doesn't exist yet.
2. The element exists, but it is not registered in DOM [in case of HTML nodes appended dynamically from Ajax responses].
3. More than one element with the same id is present which is causing a conflict.

Solutions

1. Try to access the element after its declaration or alternatively use stuff like $(document).ready();

2. For elements coming from Ajax responses, use the .bind() method of jQuery. Older versions of jQuery had .live() for the same.

3. Use tools [for example, webdeveloper plugin for browsers] to find duplicate ids and remove them.