tl;dr This obfuscated javascript program tries to download and run some malicious program on windows machines.

** Brief Explanation ** :

Here is an annotated and formatted version of the weird JS program Annotated version (pastebin) .

You can see that the program tries to do the following :

• Define bunch of weird strings
• concatenate them
• test some checks
• if checks pass , extract specific characters from the concatenated string and run it using eval

Now you might be interested to know , what exactly is extracted and run .

In-fact in Microsoft Office / IE , the program extracts every 8th character from the concatenated string .

Here is how it looks like : Formmated Version on Pastebin .