


The definition of closure is very obscure - a closure refers to a paragraph whose syntactic domain is located in a specific area and has the ability to continuously refer to (read and write) non-persistent variable values in the execution domain outside its own scope within the area. . These non-persistent variables outside the execution scope magically retain their values (deep links) when the closure was originally defined (or created). Simply put, a closure stores a copy of the variables (key-value pairs) it obtains from the upper-level function or scope in another scope, and these key-value pairs will not follow the execution of the upper-level function. Destroyed upon completion. Zhou Aimin said more clearly that closure is an "attribute table", closure is a data block, and closure is a comparison table that stores "Name=Value". It's that simple. However, it must be emphasized that closure is a runtime concept.
Closure in Javascript has two characteristics:
As a reference to a function variable - it is activated when the function returns.
A closure is a stack area that does not release resources when a function returns.
There are currently three recognized closure implementations:
with(obj){
//Here is the object closure
}
(function(){
//Function closure
})()
try{
//...
} catch(e) {
//catch closure but not in IE
}
A few useful examples
//**************** closure uniqueID****************
uniqueID = (function(){ //The calling object of this function saves the value
var id = 0; //This is the private persistent value
//The outer function returns a persistent value that has access to it The nested function
//That is the nested function we save in the variable uniqueID.
return function(){return id;}; //Return, self-increment.
})() ; //Call the outer function after definition.
document.writeln(uniqueID()); //0
document.writeln(uniqueID()); //1
document.writeln(uniqueID( )); //2
document.writeln(uniqueID()); //3
document.writeln(uniqueID()); //4
//******************closure factorial** ***********
var a = (function(n){
if(nif( n==1){ return 1; }
else{ return n * arguments.callee(n-1); }
})(4);
document.writeln(a);
function User( properties ) {
//A variable must be declared here to point to the current instance
var objthis = this;
for ( var i in properties ) {
(function(){
//Inside the closure, t is new every time, and the value of properties[i] is inside for
var t = properties[i];
objthis[ "get" i ] = function() {return t;};
objthis[ "set" i ] = function(val) {t = val;};
})();
}
}
//Test code
var user = new User({
name: "Bob",
age: 44
});
alert( user.getname());
alert( user.getage());
user.setname("Mike");
alert( user.getname());
alert( user.getage());
user.setage( 22 );
alert ( user.getname());
alert( user.getage());
Attached is the question I saw on Wuyou today:
Request:
Let this The Onclick events of the three nodes can correctly pop up the corresponding parameters.
- aa
- aa
< ;li id="a3">aa
[Ctrl A Select all Note: If you need to introduce external Js, you need to refresh to execute
My explanation is, onclick The scope of the binding function function(){alert(i)} is the corresponding li object, and the scope of i in alert is window. Each loop is rewriting the value of window.i, so after the loop is completed, i is already 4, whichever li element is clicked is 4.
Solution:
Use function closures. The code is as follows:
var lists = document.getElementsByTagName("li");
for(var i=0,l=lists.length; i lists[i].onclick = (function(i){//Save in external function
return function(){
alert(i);
}
})(i);
}
The code is as follows:
var lists = document.getElementsByTagName("li");
for(var i=0,l=lists. length; i lists[i].onclick = new function(){
var t = i;
return function(){
alert(t 1)
}
}
}
If you need to introduce external Js, you need to refresh to execute
]
var ul = document.getElementsByTagName("ul")[0];
ul.onclick = function(){
var e = arguments[0] || window.event,
target = e.srcElement ? e.srcElement : e.target;
if(target .nodeName.toLowerCase() == "li"){
alert(target.id.slice(-1))
}
[Ctrl A Select all Note:
If you need to introduce external Js, you need to refresh to execute
] The code is as follows:
var lists = document.getElementsByTagName("li");
for(var i=0,t=0,el; el = list[i++];){
el.i = t++
el.onclick = function(){
alert(this.i)
}
}
[Ctrl+A 全选 注:如需引入外部Js需刷新才能执行]
使用with语句造成的对象闭包。
var els = document.getElementsByTagName("li")
for(var i=0,n=els.length;i
els[i].onclick = function() { alert(this.innerHTML+i) };
}
[Ctrl+A 全选 注:如需引入外部Js需刷新才能执行]
使用try...catch语句构造的异常闭包:
var lists = document.getElementsByTagName("li");
for(var i=0,l=lists.length; i try{
throw i;
}catch(i){
lists[i].onclick = function(){
alert(i)
}
}
}
[Ctrl+A 全选 注:如需引入外部Js需刷新才能执行]
var els = document.getElementsByTagName("li");
(''+Array(els.length+1)).replace(/./g,function(a,i){
els[i].onclick=function(){alert(i)}
})

闭包(closure)是一个函数以及其捆绑的周边环境状态(lexical environment,词法环境)的引用的组合。 换而言之,闭包让开发者可以从内部函数访问外部函数的作用域。 闭包会随着函数的创建而被同时创建。

python闭包主要包括函数闭包和装饰器闭包。详细介绍:1、函数闭包是指在一个函数内部返回另一个函数,并且返回的函数能够访问到其内部变量。这样的返回函数就是函数闭包,函数闭包在程序中可以被反复使用,因此可以用来实现一些功能上的封装;2、装饰器闭包是指在使用装饰器时,被装饰的函数并没有直接被调用,而是被包装在一个函数内部,并返回一个新的函数。这个新的函数就是一个装饰器闭包等等。

如何利用PHP7的匿名函数和闭包实现更加灵活的代码逻辑处理?在PHP7之前,我们经常使用函数来封装一段特定的逻辑,然后在代码中调用这些函数来实现特定的功能。然而,有时候我们可能需要在代码中定义一些临时的逻辑块,这些逻辑块没有必要创建一个独立的函数,同时又不想在代码中引入太多的全局变量。PHP7引入了匿名函数和闭包,可以很好地解决这个问题。匿名函数是一种没有名

Python中的闭包是如何实现的?闭包是一种函数内部定义的函数,并且在函数内部引用了外部函数的变量。这种特性使得内部函数可以访问外部函数的变量,并且在外部函数执行完毕后,闭包仍然可以访问和操作外部函数的变量。闭包在Python中通过以下几个步骤来实现:定义外部函数,并在其中定义内部函数:首先,我们需要在外部函数内部定义一个内部函数。这个内部函数即是闭包。de

减少闭包产生的方法有避免不必要的闭包、控制闭包的返回值、使用弱引用、减少不必要的全局变量、合理使用循环和递归、使用事件代理、编写单元测试、遵循设计原则和使用工具进行代码分析等。详细介绍:1、避免不必要的闭包,在很多情况下,闭包并非必需的,可以用模块模式来实现私有变量,避免使用闭包;2、控制闭包的返回值,在使用闭包时,应该尽量控制闭包的返回值,如果闭包返回的是基本数据类型等等。

react有事件处理函数、useEffect和useCallback、高阶组件等等闭包。详细介绍:1、事件处理函数闭包:在React中,当我们在组件中定义一个事件处理函数时,该函数会形成一个闭包,可以访问组件作用域内的状态和属性。这样可以在事件处理函数中使用组件的状态和属性,实现交互逻辑;2、useEffect和useCallback中的闭包等等。

如何使用PHP7的匿名函数和闭包实现更加灵活和可复用的代码逻辑?在PHP编程领域中,匿名函数和闭包是非常有价值和强大的工具。PHP7引入了一些新的语言特性,使得使用匿名函数和闭包更加方便和灵活。本文将介绍如何使用PHP7的匿名函数和闭包来实现更加灵活和可复用的代码逻辑,并提供一些具体的代码示例。一、匿名函数匿名函数是一种没有名称的函数。在PHP中,可以将匿名

Python是一种非常流行的编程语言,因为它非常易学易用,同时也具备了强大的功能。其中,闭包是Python中的一种函数,它可以在函数的内部定义另一个函数,并返回这个函数作为函数的返回值。尽管闭包非常方便,但有时会出现某些错误,比如闭包错误。本文将介绍如何解决Python的闭包错误。初步了解闭包在Python中,闭包是由一个内部函数和一个定义在内部函数之外的函


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