Closure compiler added '--' to my Javascript function. What does it mean?

Question

I have a simple function that I ran through Google's Closure Compiler Service:

var fisherYatesShuffle = function(array) {
  var currentIndex = array.length;
  var temporaryValue;
  var randomIndex;

  // While there remain elements to shuffle...
  while (0 !== currentIndex) {

    // Pick a remaining element...
    randomIndex = Math.floor(Math.random() * currentIndex);
    currentIndex -= 1;

    // And swap it with the current element.
    temporaryValue = array[currentIndex];
    array[currentIndex] = array[randomIndex];
    array[randomIndex] = temporaryValue;
  }

  return array;
};

It gave me back the following (which I've pretty-printed):

var fisherYatesShuffle = function(a) {
  for (var b = a.length, d, c; 0 !== b;) c = Math.floor(Math.random() * b), --
    b, d = a[b], a[b] = a[c], a[c] = d;
  return a
};

What is this 'dash dash' rass at the end of line two? Why have I never seen it?

Answer 1

它是-- b --b预先递减运算符。

与

相同

b = b - 1;

它在下一行拆分，因为该行已有80个字符（最大值）。