The mysterious case of the vanishing outer closure

vanishing-closure.js

zip();
zap();
zoom();

function zip () {
	var a = 1;

	(function () {
		// v8 will remove the outer closure
		debugger;
	})();
}

function zap () {
	var a = 1;

	(function () {
		eval('console.log("Hi mom!")'); // disable v8 optimizations
		debugger;
	})()
}

function zoom () {
	var a = 1;

	(function () {
		// using a keeps the outer closure
		var b = a + 1;
		debugger;
	})()
}