Question

＆＃13;

var createShoutOuts = function(numbers_list){
  var shoutOuts = [];
  for (var j = 0; j < numbers_list.length; j++) {
    shoutOuts.push(function() {
      var shout_out = 'This is shout out number ' + (j+1);
      console.log(shout_out + '. The number is ' + numbers_list[j]);
    });		
  }
  return shoutOuts;
};

var performShoutOuts = function(user_numbers){
  var readyForShout = createShoutOuts(user_numbers);
  for (var i = 0; i < readyForShout.length; i++) {
    readyForShout[i]();
  };
};

performShoutOuts([2,4,8]);

＆＃13;

我创建了以上内容来教自己封闭。输出总是：

＆＃39;这是4号号码。号码未定义＆＃39;

我理解它总是会说4号因为被推入shoutOuts数组的匿名函数引用了j变量，而不是j变量值的副本。因此，当readyForShout[i]();调用匿名函数时，for循环已经运行，并且我的值为4.

我不明白为什么说未定义？因为在我看来，传递给performShoutOuts的数组应该存储在闭包中，因此在readyForShout[i]();执行时应该可以访问。

我错过了什么？

Answer 1

尝试使用闭包真实：

var createShoutOuts = function(numbers_list){
  var shoutOuts = [];
  for (var j = 0; j < numbers_list.length; j++) {
    shoutOuts.push((function (j) {
      return function () {
        var shout_out = 'This is shout out number ' + (j+1);
        console.log(shout_out + '. The number is ' + numbers_list[j]);
      };
    })(j));
  }
  return shoutOuts;
};

var performShoutOuts = function(user_numbers){
  var readyForShout = createShoutOuts(user_numbers);
  for (var i = 0; i < readyForShout.length; i++) {
    readyForShout[i]();
  };
};

performShoutOuts([2,4,8]);

在闭包中的未定义

1 个答案: