Avoid default dialog box for file download?
 

I have noticed, downloads of PDF files are often instructed as right-clicking and selecting the option of "Save target as ..." on some websites.

Can there be a method that could avoid the default dialog box of "open / save" from popping up, when an individual, instead of right-clicking, left clicks the link, that opens a javascript confirm box asking whether he would like to save the file or just forget about the file (press cancel button)

If this is possible, then would clicking the OK button, directly jump to downloading the file (instead of popping up the default dialog box)?

JavaScript cannot create, modify or delete any files on the machine it's being run on, so no, you can't use it to download a file.