JS examples: refactor for clarity and consistent style

Signed-off-by: Kassandra Perch <the@nodebotani.st>
Signed-off-by: Alex Tereschenko <alext.mkrs@gmail.com>

examples/javascript/isr.js

@@ -1,16 +1,18 @@
 #!/usr/bin/env node
 
-var m = require('mraa')
+"use strict";
 
-function h() {
-  console.log("HELLO!!!!")
+const mraa = require('mraa');
+
+function hello() {
+    console.log("HELLO!!!!");
 }
 
-x = new m.Gpio(14)
-x.isr(m.EDGE_BOTH, h)
+let pin = new mraa.Gpio(14);
+pin.isr(mraa.EDGE_BOTH, hello);
 
 setInterval(function() {
     // It's important to refer to our GPIO context here,
     // otherwise it will be garbage-collected
-    console.log("Waiting for an interrupt at GPIO pin " + x.getPin() + "...")
-}, 10000)
+    console.log("Waiting for an interrupt at GPIO pin " + pin.getPin() + "...");
+}, 10000);