refactor: small syntax changes

[saschanaz]

Keywords can be used as property names in ES5 so this PR removes quotes for them.

Originally I intended to use array.join() for string concatenation in writer.js and then found that it's actually slower on V8. Hmm.

 function iterate(things) {
   if (!things) return;
-  let ret = "";
-  for (const thing of things) ret += dispatch(thing);
-  return ret;
+  return things.map(dispatch).join('');
 };

[marcoscaceres]

Worth doing a release or should we sit on this for a bit?

[saschanaz]

This doesn't boost performance or add any features, so we should sit on this.