Question

我是Javascript的新手，对下面的代码片段之间的区别感到有点困惑。

摘录1：

window.onload = function() {
  var friendlyChat = new FriendlyChat();
};

摘录2：

window.onload = function() {
  window.friendlyChat = new FriendlyChat();
};

有人可以告诉他们之间的区别吗？

Answer 1

摘录1：

window.onload = function() {
  var friendlyChat = new FriendlyChat();
};

var sample = function () {
   var sampleInstance = friendlyChat; //error
   // friendlyChat cannot be accesses here as you have declared it 
   // at function scope which gets destroyed once the function has 
   // returned or completed the execution.
}

friendlyChat是一个局部变量，只能在此函数内访问。

摘录2：

window.onload = function() {
  window.friendlyChat = new FriendlyChat();
};

var sample = function () {
   var sampleInstance = friendlyChat; 
   // friendlyChat can be accesses here as you have declared it at 
   // windows scope which is available globally.
}

friendlyChat是一个全局变量，可以在任何地方访问，因为它已在根级别声明，即窗口。

以下js代码段之间的区别

1 个答案: