Weird JavaScript syntax I've never used before, but it works

Question

Do you know why this code compiles and what is something?

function Box() {
  something: {
    alert(1);
  }
}

var box = new Box();

Answer 1

That's a javascript label.

It is used to break or continue nested loops.

Here is the doc: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label

// Example code
myLoop:for (var i = 0; i < 10; ++i)
    for (var j = 0; j < 10; ++j)
        if (whatever)
            break myLoop;

Answer 2

That is a label.

They are used in combination with break and continue to choose which loop the statement should apply to when you have nested loops.

It is pointless where it is.