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Counter 是独立的吗?

在这儿我们用相同的 makeCounter 函数创建了两个计数器(counters):countercounter2

它们是独立的吗?第二个 counter 会显示什么?0,12,3 还是其他?

function makeCounter() {
  let count = 0;

  return function() {
    return count++;
  };
}

let counter = makeCounter();
let counter2 = makeCounter();

alert( counter() ); // 0
alert( counter() ); // 1

*!*
alert( counter2() ); // ?
alert( counter2() ); // ?
*/!*