Chrome Extension for switching between header (.h) and source files (.m,.mm,.c,.cpp) on GitHub with the Xcode Shortcut Ctrl+Command+Up

main.js

chrome.commands.onCommand.addListener(function(command) {

	chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
		
		var current = tabs[0];
		var url = current.url;
		var ext = url.substring(url.lastIndexOf("."));

		if(ext === ".h")
		{
			existingSourceFileForHeaderURL(url, function (sourceURL) {

				if(sourceURL)
				{
					chrome.tabs.update(current.id, { url: sourceURL });
				}
			});
		}
		else if(ext === ".m" || ext === ".c" || ext === ".cpp" || ext === ".mm")
		{
			var headerURL = replaceExtension(url, "h");
			chrome.tabs.update(current.id, { url: headerURL });
		}
	});
});

function urlExists(url, callback) {

    var http = new XMLHttpRequest();
    http.open('HEAD', url);
    http.onreadystatechange = function() {

        if (this.readyState == this.DONE) {
            callback(this.status != 404);
        }
    };

    http.send();
}

function replaceExtension(url, newExt) {

	var withoutExt = url.substring(0, url.lastIndexOf(".") + 1);
	return withoutExt + newExt;
}

function existingSourceFileForHeaderURL(url, callback) {

	var objcURL = replaceExtension(url, "m");
	urlExists(objcURL, function (exists) {

		if(exists)
		{
			callback(objcURL);
		}
		else
		{
			var mmURL = replaceExtension(url, "mm");
			urlExists(mmURL, function (exists) {

				if(exists)
				{
					callback(mmURL);
				}
				else
				{
					var cURL = replaceExtension(url, "c");
					urlExists(cURL, function (exists) {

						if(exists)
						{
							callback(cURL);
						}
						else
						{
							var cppURL = replaceExtension(url, "cpp");
							urlExists(cURL, function (exists) {

								if(exists)
								{
									callback(cppURL);
								}
								else
								{
									callback(null);
								}
							});
						}
					});
				}
			});
		}
	});
}

manifest.json

{
  "name": "HeaderImpl",
  "version": "1.0",
  "description": "Switch between Header and Implementation Files using a Keyboard Shortcut",
  "background": {
    "persistent": false,
    "scripts": [ "main.js" ]
  },
  "permissions": [ "tabs", "https://github.com/" ],
  "commands": {
    "switch-to-other-file": {
      "suggested_key": {
        "default": "Ctrl+Shift+Up",
        "mac": "MacCtrl+Command+Up"
      },
      "description": "Switch to the other file"
    }
  },
  "manifest_version": 2
}