Fixes #35 - Progressively enhance install button with appropriate links and text

static/js/index.js

Index: static/js/index.js
===================================================================
new file mode 100644
--- /dev/null
+++ b/static/js/index.js
@@ -0,0 +1,57 @@
+"use strict";
+
+(function()
+{
+  var supportedPlatforms = {
+
+    // Desktop browsers
+    "chrome": "https://chrome.google.com/webstore/detail/cfhdojbkjhnklbpkdaibdccddilifddb",
+    "opera": "https://addons.opera.com/extensions/details/opera-adblock/?display=en-US",
+    "yandexbrowser": "https://chrome.google.com/webstore/detail/cfhdojbkjhnklbpkdaibdccddilifddb",
+    "msie": "https://update.adblockplus.org/latest/adblockplusie.exe",
+    "msedge": "https://www.microsoft.com/store/p/adblock-plus/9nblggh4r9nz",
+    "firefox": "https://update.adblockplus.org/latest/adblockplusfirefox.xpi",
+    "safari": "https://update.adblockplus.org/latest/adblockplussafari.safariextz",
+    "maxthon": "",
+
+    // Mobile platforms
+    "ios": "https://eyeo.to/adblockbrowser/ios/abp-website",
+    "android": "https://eyeo.to/adblockbrowser/android/abp-website"
+  };
+
+  function setupHeroDownloadButton()
+  {
+    var detectedPlatform = Object.keys(supportedPlatforms)
+      .find(bowser.hasOwnProperty.bind(bowser));
+
+    if (!detectedPlatform) return;
+
+    document.body.classList.add(detectedPlatform);
+
+    if (detectedPlatform == "maxthon") return;
+
+    var heroDownloadButton = document.getElementById("hero-download-button");
+    heroDownloadButton.href = supportedPlatforms[detectedPlatform];
+    heroDownloadButton.innerHTML = document

[juliandoucette, 2018/04/16 15:44:41]

NIT/Suggest: innerText (we don't support IE 8 anymore and it's ~more secure?)

[ire, 2018/04/16 16:00:59]

Changed to textContent which seems to be better for performance 

(https://developer.mozilla.org/en-US/docs/Web/API/Node/textContent,
https://developer.mozilla.org/en-US/docs/Web/API/Node/textContent)

[juliandoucette, 2018/04/16 16:12:58]

Thanks!

(Facepalm: I meant to say textContent. My unconsciously wrote the last thing I
read by mistake.)

+      .getElementById("hero-download-button-template-" + detectedPlatform)
+      .innerHTML;
+    
+    heroDownloadButton.addEventListener("click", function(event)
+    {
+      if (typeof chrome == "undefined") return;
+      event.preventDefault();
+
+      try

[juliandoucette, 2018/04/16 15:44:41]

TOL: Why are curly braces required for try/catch statements :/?

[ire, 2018/04/16 16:00:59]

I know right?!?! Maybe there's a good reason I don't know about

+      {
+        chrome.webstore.install();
+      }
+      catch(error)
+      {
+        window.location = "/" + this.hreflang + "/download";
+      }
+    });
+  }
+
+  if (typeof bowser != "undefined") setupHeroDownloadButton();
+
+}());