eval() in closure with subsequent read-write access to closure

eval-in-closure-ext.js

function bindClosureSlot( name ) {
	return "function(v){ if( arguments.length<1 ) return " + name + "; else return " + name + "=v; }";
}

function evalInClosureExt( code, closure ) {
	return Function.apply( 
		null,
		Object.keys( closure ).concat(
			"return [" +
				code + "," +
				"{" +
					Object.keys( closure ).map(
						function( k ) {
							return k + ":" + bindClosureSlot( k );
						}
					).join(",") +
				"}" +
			"];"
		)
	).apply(
		null,
		Object.keys( closure ).map( function(k){ return closure[k]; } )
	)
}

console.log( "Test 1" );

var ext_fn = evalInClosureExt(
		"function(){ return x++; }",
		{ x: 5 }
	),
	fn = ext_fn[0],
	closure = ext_fn[1];

console.log( "x = ", closure.x() );
console.log( "fn() = ", fn() );
console.log( "x = ", closure.x() );
console.log( "x = ", closure.x( 10 ) );
console.log( "fn() = ", fn() );
console.log( "x = ", closure.x() );