JavaScript 和 Facebook - 语法解释

发布于 2024-11-09 02:25:03 字数 560 浏览 0 评论 0原文

我对 JavaScript 和 Facebook SDK 完全陌生。有人可以用英语描述以下特征：

  window.fbAsyncInit = function() {
    FB.init({appId: 'your app id', status: true, cookie: true,
             xfbml: true});
  };
  (function() {
    var e = document.createElement('script'); e.async = true;
    e.src = document.location.protocol +
      '//connect.facebook.net/en_US/all.js';
    document.getElementById('fb-root').appendChild(e);
  }());

即用英语“阅读”此内容的标准方式。 “(function (){”位是我摔倒的地方。我可以看到它在做什么：运行这个位后，异步继续并执行 function() 中的内容，但这是什么 JavaScript 功能以及组件是什么？

原文

I am totally new to JavaScript and the Facebook SDK. Could someone describe in English the following feature:

  window.fbAsyncInit = function() {
    FB.init({appId: 'your app id', status: true, cookie: true,
             xfbml: true});
  };
  (function() {
    var e = document.createElement('script'); e.async = true;
    e.src = document.location.protocol +
      '//connect.facebook.net/en_US/all.js';
    document.getElementById('fb-root').appendChild(e);
  }());

i.e. the standard way of "reading" this in English. The "(function (){" bit is where I fall over. I can see what it's doing: after running this bit async goes on and does the stuff in function(), but what JavaScript feature is this and what are the components?

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战皆罪 2024-11-16 02:25:03

语法有点奇怪。第一个位

window.fbAsyncInit = function() {
  FB.init({appId: 'your app id', status: true, cookie: true,
           xfbml: true});
};

是一个函数表达式。在其使用上下文中，开发人员还可以编写：

function fbAsyncInit() {
  FB.init({appId: 'your app id', status: true, cookie: true,
           xfbml: true});
};

请参阅 this JSFiddle 以获得等效内容。无论哪种方式，调用都是相同的：

fbAsyncInit();

以下代码：

  FB.init({appId: 'your app id', status: true, cookie: true,
           xfbml: true});

在 FB 对象上调用 Init 函数并传递对象文字作为参数。

这里需要更多的解释：

(function() {
  var e = document.createElement('script'); e.async = true;
  e.src = document.location.protocol +
    '//connect.facebook.net/en_US/all.js';
  document.getElementById('fb-root').appendChild(e);
}());

这篇文章可能会有所帮助： JavaScript/jQuery 语法是什么意思？

JavaScript 中的所有变量都被“提升”到全局范围，除非它们位于函数中。您看到的约定是自动调用的匿名函数。我们可以写：

function MyFunc(){
  var e = document.createElement('script'); e.async = true;
  e.src = document.location.protocol +
    '//connect.facebook.net/en_US/all.js';
  document.getElementById('fb-root').appendChild(e);
};
MyFunc();

但这会在内存中产生额外的代码和额外的变量。

The syntax is a little strange. The first bit

window.fbAsyncInit = function() {
  FB.init({appId: 'your app id', status: true, cookie: true,
           xfbml: true});
};

Is a function expression. In the context of its use, the developer could also have written:

function fbAsyncInit() {
  FB.init({appId: 'your app id', status: true, cookie: true,
           xfbml: true});
};

See this JSFiddle for an equivalent. Either way, calling is identical:

fbAsyncInit();

the following code:

  FB.init({appId: 'your app id', status: true, cookie: true,
           xfbml: true});

Is calling the Init function on the FB object and passing an object literal as a parameter.

This bit here takes a little more explanation:

(function() {
  var e = document.createElement('script'); e.async = true;
  e.src = document.location.protocol +
    '//connect.facebook.net/en_US/all.js';
  document.getElementById('fb-root').appendChild(e);
}());

This article might help: What does this JavaScript/jQuery syntax mean?

All variables in JavaScript are 'hoisted' to global scope unless they are in a function. The convention you see is an anonymous function that is automatically invoked. We could have written:

function MyFunc(){
  var e = document.createElement('script'); e.async = true;
  e.src = document.location.protocol +
    '//connect.facebook.net/en_US/all.js';
  document.getElementById('fb-root').appendChild(e);
};
MyFunc();

But that would have been extra code and extra variables in memory.

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