let 声明块变量

• let declarations are scoped to blocks as well as functions.
  let 声明的作用域为块和函数。
• let declarations can only be accessed after the line of declaration is reached (see temporal dead zone (opens in a new tab)). For this reason, let declarations are commonly regarded as non-hoisted (opens in a new tab).
  let 声明只能在到达声明行后才能访问（请参阅临时死区）。因此， let 声明通常被视为非提升声明。
• let declarations do not create properties on globalThis (opens in a new tab) when declared at the top level of a script.
  在脚本顶层声明时， let 声明不会在 globalThis 上创建属性。
• let declarations cannot be redeclared (opens in a new tab) by any other declaration in the same scope.
  let 声明不能被同一范围内的任何其他声明重新声明。
• let begins declarations, not statements (opens in a new tab). That means you cannot use a lone let declaration as the body of a block (which makes sense, since there's no way to access the variable).
  let 开始声明，而不是语句。这意味着您不能使用单独的 let 声明作为块的主体（这是有道理的，因为无法访问该变量）。