为什么要为命名变量分配函数声明？

Question

编辑:它不是对命名变量的函数声明的赋值 - 检查接受的答案.保留标题,因为其他人可能会犯同样的错误.

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在阅读Paul Irish的infinitescroll jquery插件代码时,我偶然发现了以下模式:

...
_create : function infscr_create (options, callback) { /* ... */ },
...

这样做的好处是什么,而不是:

...
_create : function (options, callback) { /* ... */ },
...

Answer 1

它的好处(称为"命名函数表达式")是该函数具有实际名称.在您的第二个版本中,该属性具有名称,但该功能没有.给函数实际名称可以帮助您的工具帮助您(调用堆栈列表,断点列表等)更多:Anonymousouses anonymous

它的缺点是它在一些破坏的JavaScript引擎中有意想不到的结果,比如IE8和更早版本的引擎.在IE8及更早版本中,Paul Irish的版本在两个完全不同的时间创建了两个独立的功能.但这并不是一个问题,除非你保留并使用对它们的引用,并期望它们是相同的函数(例如,当挂钩和取消挂钩事件处理程序时).鉴于它是保罗,我猜他肯定不会这样做.

重新提问你的问题标题:请注意,这不是一个函数声明,但你可以原谅它,因为它看起来几乎就像一个.:-)这是一个函数表达式.函数声明和函数表达式发生在完全不同的时间,并且对它们的创建范围产生不同的影响.

只是为了完整性:

// This is a function declaration -- note that it's not a "right-hand
// value", e.g., we're not using the result of it immediately (via an
// assignment, a property initializer, calling it, or passing it into
// a function as an argument -- none of those).
//
// Declarations happen upon entry to the scope (not as part of step-by-
// step code). The function's name is added to the scope in which it's
// declared. Declarations are illegal inside branches (`if`, `try/catch`,
// `for`, etc.), but some engines will rewrite them as expressions for
// you if you do that. Others will not, they'll just always declare the
// function regardless of whether the code was reached. So don't do that.
function foo() {
}

// These are all anonymous function expressions. The function in the
// expression has no name, although some debuggers are pretty smart
// about looking at the expression and (where they can) listing a
// kind of pseudo-name for the function. Others are not that smart,
// which is why I avoid anonymous functions.
//
// Expressions happen when they're reached in step-by-step code.
var f = function() { };
var obj = {
    prop: function() { }
};
doSomethingCoolWithAFunction(function() { });
(function() { })(); // Call it immediately
!function() { }();  // Call it immediately
~function() { }();  // Call it immediately, there are a few variants

// These are all *named* function expressions.
//
// Since they're expressions, they happen when they're reached in the
// step-by-step code. The function's name is NOT added to the containing
// scope (except by engines with bugs).
//
// These are the same examples as above, but with a name. No other changes.
var f = function foo() { };
var obj = {
    prop: function foo() { }
};
doSomethingCoolWithAFunction(function foo() { });
(function foo() { })(); // Call it immediately
!function foo() { }();  // Call it immediately
~function foo() { }();  // Call it immediately, there are a few variants

Answer 2

1. 该函数有一个名称,而不是一个匿名函数; 这显示在调试跟踪中,使调试更容易.
2. 该函数可以通过调用来调用自身 infscr_create()