javascript 函数声明的范围
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javascript scope of function declarations
提问by user1816847
The varkeyword in javascript causes a variable to be stored in the local scope. Without varvariables belong to the global scope. What about functions? It's clear what happens when functions are declared like variables
varjavascript 中的关键字导致将变量存储在本地范围内。没有var变量属于全局范围。函数呢？很明显当函数像变量一样声明时会发生什么
var foo = function() {...}
but what scope does
但范围是什么
function foo() {...}
belong to?
属于？
EDIT: I realized I didn't ask quite the right question so as a follow up. In the outer most nesting is there a difference between the above two declarations and the following declaration?
编辑：我意识到我没有问正确的问题所以作为跟进。在最外层的嵌套中，上面两个声明和下面的声明有区别吗？
foo = function() {...}
回答by bfavaretto
It belongs to the currentscope, always. For example:
它始终属于当前范围。例如：
// global scope
// foo is a global function
function foo() {
// bar is local to foo
function bar() {
}
}
Regarding your second question, this:
关于你的第二个问题，这个：
foo = function() {...}
is an anonymous function expression assigned to a global variable (unless you're running is strict mode, then foowould be undefined). The difference between that and function foo() {}is that the latter is a function declaration(versus a variabledeclaration, which is assigned an anonymous function expression).
是分配给全局变量的匿名函数表达式（除非您在严格模式下运行，否则foo将是未定义的）。两者之间的区别在于function foo() {}后者是一个函数声明（相对于变量声明，它被分配了一个匿名函数表达式）。
You might be interested in this excellent article about function declarations and function expressions: Named function expressions demystified.
您可能对这篇关于函数声明和函数表达式的优秀文章感兴趣：命名函数表达式解密。
回答by Bergi
Function declarations are always local to the current scope, like a variable declared with the varkeyword.
函数声明总是局部于当前作用域，就像用var关键字声明的变量一样。
However, the difference is that if they are declared(instead of assigned to a variable) their definition is hoisted, so they will be usable everywhere in the scope even if the declaration comes in the end of the code. See also var functionName = function() {} vs function functionName() {}.
但是，不同之处在于，如果它们被声明（而不是分配给变量），它们的定义会被提升，因此即使声明出现在代码的末尾，它们也可以在范围内的任何地方使用。另请参阅var functionName = function() {} 与 function functionName() {}。
回答by deck
Noteworthy distinction taking implicit globals into account:
考虑到隐式全局变量的值得注意的区别：
var foo = function() {
// Variables
var myVar1 = 42; // Local variable
myVar2 = 69; // Implicit global (no 'var')
// Functional Expressions
var myFn1 = function() { ... } // Local
myFn2 = function() { ... } // Implicit global
function sayHi() {
// I am a function declaration. Always local.
}
}
Hopefully that clarifies a little. Implicit globals are defined if you forget a varbefore your assignment. Its a dangerous hazard that applies to variable declarations and functional expressions.
希望这能澄清一点。如果您var在分配之前忘记了 a ，则会定义隐式全局变量。它是适用于变量声明和函数表达式的危险危险。
回答by Andrew Hymanman
Your first example (var foo = function() {...}) is called an anonymous function. It is dynamically declared at runtime, and doesn't follow the same rules as a normal function, but follows the rules of variables.
您的第一个示例 ( var foo = function() {...}) 称为匿名函数。它是在运行时动态声明的，不遵循与普通函数相同的规则，而是遵循变量的规则。
