How to detect if a web page is running from a website or local file system

Question

I'm a newbie to javascript. How can I detect if my javascript is being run from a web site (http://) vs a local file.

Answer 1

switch(window.location.protocol) {    case 'http:':    case 'https:':      //remote file over http or https      break;    case 'file:':      //local file      break;    default:       //some other protocol } 

Answer 2

For testing different 'kinds' of local, all at once:

// Returns the page location type // 0 (falsey) = Local file, direct from disk (file://path/to/file.html) // 1 (truthy) = Virtually remote file, from local server (http://localhost) // 2 (truthy) = Remote file from remote server (http://example.com)  function locationType(){     if( window.location.protocol == 'file:' ){ return 0; }     if( !window.location.host.replace( /localhost|127\.0\.0\.1/i, '' ) ){ return 2; }     return 1; } 

Rationale: you may want to test for whether the page is a) on a remote server, or b) on a local server (same computer, for testing, like with AMP), or c) a local file, retrieved directly from disk via the "file://" protocol.

Note that this doesn't handle every possible edge case. For example, you can technically redirect different IPs to "localhost", and other non-"file://" schemes (like "foo://") may in fact represent local access. But it works for most cases and can be otherwise tweaked as needed

Testing only for "http" and "https" is a bit limited, since there are dozens of other LAN and WAN network schemes in use around the world. Whether or not they're local or can even use HTML/JS code may vary, of course (IANA URI Schemes).