JavaScript 闭包深入浅出

//1，闭包

$(document).ready(function(){
var spans=$("#divTest span");
for(var i=0;i<spans.length;i++){
spans[i].onclick=function(){
alert(i);
}
}
}); 
$(document).ready(function(){
var spans2=$("#divTest2 span");
var spans=$("#divTest span");
for(var i=0;i<spans2.length;i++){
(function(num){
spans2[i].onclick=function(){
alert(num);
}
})(i);
spans[i].onclick=function(){
alert(i);
}
}
}); 

//2,内部函数 ，在outerFn作用域内调用innerFn是有效的，而在outFn外部调用innerFn则是无效的。

function outerFn () {
document.write("Outer function</br>");
function innerFn(){
document.write("Inner function</br>");
}
innerFn();
}
outerFn();

//3,

var globalVar;
function outerFn () {
document.write("Outer function</br>");
function innerFn(){
document.write("Inner function</br>");
}
globalVar=innerFn;
}
outerFn();
globalVar();

//返回值的方式

function outerFn(){
document.write("Outer function</br>");
function innerFn(){
document.write("Inner function</br>");
}
return innerFn;
}
var fnRef=outerFn();
fnRef();

//只要存在调用内部函数的肯能，JavaScript就会保留呗引用的函数。而且Javascript运行时需要跟踪引用这个内部函数的所有变量，知道最后一个变量废弃，JavaScript的垃圾收集器才能释放相应的内存空间。闭包是指：有权限访问另一个函数作用域的变量的函数。
// 4，变量作用域

function outerFn(){
document.write("Outer function</br>");
function innerFn(){
var innerVar=0;
innerVar++;
document.write("Inner function	");
document.write("innerVar = "+innerVar+"</br>");
}
return innerFn;
}
var fnRef=outerFn();
fnRef();
fnRef();
var fnRef2=outerFn();
fnRef2();
fnRef2();

var globalVar=0;
function outerFn(){
document.write("Outer function</br>");
function innerFn(){
globalVar++;
document.write("Inner function	");
document.write("globalVar = "+ globalVar +"</br/>");
}
return innerFn;
}
var fnRef=outerFn();
fnRef();
fnRef();

var fnRef2=outerFn();
fnRef2();
fnRef2();

　　

function outerFn(){
var outerVar=0;
document.write("Outer function<br/>");
function innerFn(){
outerVar++;
document.write("Inner function	");
document.write("outerVar = "+outerVar+ "<br/>");
}
return innerFn;
}
var fnRef=outerFn();
fnRef();
fnRef();

var fnRef2=outerFn();
fnRef2();
fnRef2();

function outerFn(){
var outerVar=0;
document.write("Outer function</br>");
function innerFn1(){
outerVar++;
document.write("Inner function 1 	");
document.write("outerVar = "+ outerVar+"</br>" );
}
function innerFn2(){
outerVar+=2;
document.write("Inner function 2 	");
document.write("outerVar = "+ outerVar+"</br>" );
}
return {"fn1":innerFn1,"fn2":innerFn2};
}

var fnRef=outerFn();
fnRef.fn1();
fnRef.fn2();
fnRef.fn1();
var fnRef2=outerFn();
fnRef2.fn1();
fnRef2.fn2();
fnRef2.fn1();

//5,闭包之间的交互

// 对outerFn的后续调用会创建这些闭包的新实例，同时也会创建新的封闭环境，本质上是创建了一个新对象，自由变量就是这个实例的对象变量，而闭包就是这个对象的实例方法。