Javascript code to validate filename before client upload

I want this validation to check for three things if possible - and the order of importance to me is: 1. Invalid characters in the file name e.g. spaces, '/', '\', '(', ')' etc (may well be some others) 2. File name too long - maybe a max of 25 characters or so - to be decided. 3. Only certain permitted file types/extensions e.g. PDF,JPG,PNG,DOC etc 4. Max file size (this isn't a critical rule if it's difficult to achieve) Any breach of the 'rules' will pop up an alert message that suits the particular rule breach. The code is to be inserted into existing HTML file that is using: <FORM method=post enctype="multipart/form-data" action=uploadfile> Obviously, we don't want any upload to be allowed to occur until the client renames the file, or chooses another, or decides not to proceed. UPDATE 1. 1. In regards to Item (1) Invalid characters in file name, I'd like to change this such that the script checks that the file name ONLY contains these characters: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z a b c d e f g h i j k l m n o p q r s t u v w x y z 0 1 2 3 4 5 6 7 8 9 . _ - 2. Regarding Item (4), it seems that assessing MAX file size isn't easily achievable, so let's delete that. UPDATE 2 I want to be fair and avoid unannounced 'scope creep', so here's another clarification/update. 1. Blank spaces in a file name are a problem, so we want those screened too, BUT separately 'called out' in the pop-up Alert (example below). 2. In the Alert pop-up, if there is more than one issue, and disallowed file type is one of those issues, then it should be the first issue mentioned - see example below. 3. There should only be one Alert pop-up - and it should contain the details of the issues identified - see example. Example of Alert pop-up for a file that has every issue, but only the issues applicable to the file in question should be included: There are problems with the file you're trying to upload. 1. The file type you're trying to upload is not of a permitted type. For the protection of our clients systems, only these files are permitted: for documents: PDF, for images: JPEG, JPG, PNG Word documents and Excel spreadsheet documents are not allowed due to the inherent danger of malicious content. 2. The name of your file contains invalid characters. Only these characters are allowed: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z a b c d e f g h i j k l m n o p q r s t u v w x y z 0 1 2 3 4 5 6 7 8 9 . _ - Please re-name your file and try again. 3. There are 'spaces' in the name of your file - these need to be removed by re-naming your file and trying the upload again. 4. The name of your file is too long - a maximum of 25 characters is permitted. Please re-name your file and try the upload again. If you need any assistance regarding a document, contact your Body Corporate Manager - they'll be able to assist.