让 let 替换匿名闭包以获得私有变量吗？

Question

如果你想在 JavaScript 中有某种私有变量，你可以将代码放在匿名闭包中，对吧？现在既然包含了 let，闭包的这个特定用例就消失了吗？还是它仍然相关？

顶级示例：

// global variable a
var a = 6;

// using let
{
  // new variable a that only lives inside this block
  let a = 5;
  console.log(a); // => 5
}

console.log(a); // => 6

// using a closure
(function() {
  // again a new variable a that only lives in this closure
  var a = 3;
  console.log(a); // => 3
})();

console.log(a); // => 6

Answer 1

在Javascript中有一个叫做Hoisting的东西，"hoists"上面的变量甚至在初始化之前。

// global variable a
var a = 6;

// using let
{
  // new variable a that only lives inside this block
  let a = 5;
  console.log(a); // => 5
}

console.log(a); // => 6

// using a closure
(function() {
  // again a new variable a that only lives in this closure
  var a = 3;
  console.log(a); // => 3
})();

console.log(a); // => 6

因此此代码更改为：

// The global variable 'a' is hoisted on the top of current scope which is Window as of now
var a;

// Initialization takes place as usual
a = 6;


// This is a block
{

  // This local variable 'a' is hoisted on the top of the current scope which is the 'block'
  let a;

  a = 5;
  console.log(a); // => 5
}

console.log(a); // => 6

// Using an IIFE
(function() {

  // This local variable 'a' is hoisted on the top of the current scope which is the block of IIFE
  var a;

  a = 3;
  console.log(a); // => 3
})();

console.log(a); // => 6

Pre ES6 我们曾经使用 IIFEs to make variables which would not pollute the global scope, but after ES6 we generally use let and const because they provide block-scope.

让 let 替换匿名闭包以获得私有变量吗？

Does let replace anonymous closures for having private variables?

javascript

ecmascript-5