The ?. operator from C# for JavaScript via Sweet.js

null-guard.sjs

// This version allows LHS to be any expression
// (and makes sure it's only evaluated once by storing the result)

let (?.) = macro {
	rule infix { $lhs:expr | $rhs:ident } => {
		(function ($tmp) {
			return $tmp === null ? null : $tmp.$rhs;
		})($lhs)
	}
}

function bar() {
	return {
		a: 'a',
		baz: {
			notB: 'not b'
		}
	};
}

var foo = bar()?.baz?.b;

console.log(foo);