js: Default to linux-amd64 and fix split() call on platform (#187)

In certain cases where the platform cannot be automatically determined, we should at least populate a default so that the download page doesn't break.

src/download.html

@@ -23,8 +23,7 @@
 				<div>
 					<div>
 						<b>Platform:</b>
-						<select size="1" id="platform">
-							<option></option>
+						<select size="1" id="platform" selected="linux-amd64">
 							<option value="dragonfly-amd64">Dragonfly amd64</option>
 							<option value="freebsd-amd64">FreeBSD amd64</option>
 							<option value="freebsd-arm-6">FreeBSD arm 6</option>

src/resources/js/download.js

@@ -169,11 +169,11 @@ $(function() {
 	});
 })
 
-// autoPlatform choooses the platform in the list that best
+// autoPlatform chooses the platform in the list that best
 // matches the user's browser, if it's available.
 function autoPlatform() {
 	// assume 32-bit linux, then change OS and architecture if justified
-	var os = "linux", arch = "386", arm = "";
+	var os = "linux", arch = "amd64", arm = "";
 
 	// change os
 	if (/Macintosh/i.test(navigator.userAgent)) {
@@ -215,11 +215,15 @@ function autoPlatform() {
 }
 
 function getDownloadLink() {
+	// make sure we at least have a default,
+	// in the case that autoPlatform() failed
+	var platformString = $('#platform').val();
+	if (!platformString) {
+		platformString = "linux-amd64"
+	}
+
 	// get platform components
-	var platformParts = $('#platform').val().split("-");
-	var os = platformParts[0];
-	var arch = platformParts[1];
-	var arm = platformParts.length > 2 ? platformParts[2] : "";
+	var [os, arch, arm = ""] = platformString.split("-");
 
 	var qs = new URLSearchParams();
 	if (os)   qs.set("os", os);