Elm version 0.17.1
macOS Sierra version 10.12
Opera 40.0.2308.81

This project is for elucidation of an Elm compiler bug. I reported it in the elm-compiler project as issue #1510.

Build index.js with:

elm make default-in-port-record.elm --output index.js

Then open index.html in your browser.

Cick the "Click Me" button once. Note that the "default" value increments.

Refresh your browser. You'll get a JavaScript runtime error in the function initWithFlags in index.js.

The problem is that "default" is a reserved word in JavaScript. The compiler correctly escapes it by prepending a "$" in most of the code, e.g. here's the compiler output for the update function:

var _user$project$Main$update = F2(
	function (msg, model) {
		var _p0 = msg;
		return {
			ctor: '_Tuple2',
			_0: _elm_lang$core$Native_Utils.update(
				model,
				{$default: model.$default + 1}),
			_1: _elm_lang$core$Platform_Cmd$none
		};
	});

The compiler does not properly escape it, however in the code the converts it from Elm to JavaScript for saving (when you click the "Click Me" button and updateWithStorage invokes the setStorage port):

var _user$project$Main$setStorage = _elm_lang$core$Native_Platform.outgoingPort(
	'setStorage',
	function (v) {
		return {default: v.default};
	});