Do standalone JavaScript blocks have any use?

问题

The MDN article on JavaScript blocks gives this example:

var x = 1;
{
  var x = 2;
}
alert(x); // outputs 2

As you can see JavaScript doesn't have block scope. So are there any good use cases for standalone blocks in JavaScript?

By "standalone" I mean not paired with a control flow statement (if, for, while, etc.) or a function.

回答1:

Short answer: ...not really.

The only use I know for them is labels:

myBlock: {
    // stuff
    if (something) break myBlock // jump to end of block
    // more stuff
    if (somethingElse) continue myBlock // jump to beginning of block
    // blah blah blah, more stuff
}

(almost like a goto, better watch out for the raptors)

Needless to say, this is a very bad idea. So basically, nothing; just don't use them.

(side note: a do { /* stuff */ if (something) break; /* stuff */ } while (false) could do the same thing)

回答2:

ES2015 introduces block scoping with let and const, so standalone blocks become useful for limiting the scope of variables:

{
  let privateValue = 'foo';
}

console.log(privateValue); // -> ReferenceError

In contrast to var:

{
  var privateValue = 'foo';
}

console.log(privateValue); // -> "foo"

let and const are implemented in the latest versions of all major browsers (including IE11).

• let compatibility table
• const compatibility table

来源：https://stackoverflow.com/questions/17939230/do-standalone-javascript-blocks-have-any-use