The Modern JS Tutorial: Variable scope and Closure: counter object

	function Counter() {
	let count = 0;
	this.up = function() {
	return ++count;
	};
	this.down = function() {
	return --count;
	};
	}
	let counter = new Counter();
	console.log( counter.up() ); // ?
	console.log( counter.up() ); // ?
	console.log( counter.down() ); // ?
	// Answer: 1
	// Answer: 2
	// Answer: 1
	// it has same lexical environment

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