嵌入函数问题

发布于 2024-10-08 14:27:00 字数 421 浏览 5 评论 0原文

例如：

//global vars
var g1,g2,g3;
function a(p1,p2,p3){
  //local vars
  var a1,a2,a3;
  return function(){
    //an embed function, looks like dynamic defined at runtime
  }
}

var f1 = a(1,2,3)
var f2 = a(4,5,6)
f1()
f2()

我的问题是，f1和f2是否指向内存中的相同代码，为什么它们接缝不同的函数？每次调用 a 时，函数 a 是否都会花费时间来创建嵌入函数？

而且GC的工作方式也很有趣，a执行完后，a的局部变量不会被GC，而必须是返回的embed函数被GC后才被GC，因为返回的embed函数仍然可以调用函数a的局部变量。

原文

for example:

//global vars
var g1,g2,g3;
function a(p1,p2,p3){
  //local vars
  var a1,a2,a3;
  return function(){
    //an embed function, looks like dynamic defined at runtime
  }
}

var f1 = a(1,2,3)
var f2 = a(4,5,6)
f1()
f2()

my question is , is f1 and f2 point to the same code in memory, why they seams diffrent function? does function a spend time to create the embed function when a is call each time?

and GC works also very intresting, local vars of a will not be GC after a executed, It must be GC after the returned embed function GCed, cause of returned embed function still can invoke the local vars of function a.

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梦与时光遇 2024-10-15 14:27:00

回答你的问题：

不，它们指向不同的函数
当然，创建新函数需要一点时间
这是因为返回的函数是闭包，并且仍然可以引用它们创建的范围。

函数之间的差异语句和表达式

function foo() {} // created at compile time, is available every in the code from the start

var foo = function() {}; // created at runtime, only is available after it's creation
                         // while foo already exists it's set to undefined

function test() {
    return function(){}; // returns a new function each time test is called
}

闭包

function test() {
    var b = 123;

    // this function inherits all outer scopes so it still has access to b
    return function() {
        console.log(b); //
    };
}

有关闭包的更多信息，请参阅此问题和答案。

To answer your questions:

No they point to different functions
Of course it take a little time to create the new functions
That is because the returned functions are closures and can still reference the scope in which they were created in.

Difference between Function Statement and Expression

function foo() {} // created at compile time, is available every in the code from the start

var foo = function() {}; // created at runtime, only is available after it's creation
                         // while foo already exists it's set to undefined

function test() {
    return function(){}; // returns a new function each time test is called
}

Closures

function test() {
    var b = 123;

    // this function inherits all outer scopes so it still has access to b
    return function() {
        console.log(b); //
    };
}

For more on closures see this question and the answers.

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