IntelliJ IDEA: json file syntax

I am using IntelliJ IDEA 14 for a web project, where I want to keep a file a.js containing a JSON object. The content of the a.js is

{
    "ac" : "abc",
    "d" : 4,
    "_constants": {}
}

While editing this file, IntelliJ keeps reminding me that this file has syntactic errors. It makes a hints after "ac", "d" and "_constants", before the semicolon, saying "Expecting newline or semicolon".

Does not IntelliJ IDEA accept a file containing a JSON object as a legitimate javascript file?