javascript 嵌套函数

最新推荐文章于 2024-11-23 20:26:18 发布

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文章标签：

#javascript #function #accessor #closures #each #string

本文探讨了JavaScript中嵌套函数的概念，展示了如何利用闭包返回函数指针，并且通过实例详细解释了如何使用闭包实现类的封装，包括私有属性的设置与获取。

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8.8.4. Nested Functions as Closures

1、执行嵌套函数（方法）


var x = "global";



function f() {



    var x = "local";



    function g() { alert(x); }



    g();



}



f();  // Calling this function displays "local"







2、返回函数指针



// This function returns a function each time it is called



// The scope in which the function is defined differs for each call



function makefunc(x) {



    return function() { return x; }



}







// Call makefunc() several times, and save the results in an array:



var a = [makefunc(0), makefunc(1), makefunc(2)];







// Now call these functions and display their values.



// Although the body of each function is the same, the scope is



// different, and each call returns a different value:



alert(a[0]());  // Displays 0



alert(a[1]());  // Displays 1



alert(a[2]());  // Displays 2



3、闭包（简单来讲，通过函数嵌套实现类的封装。即私有（private)属性需通过公用(public)方法赋值与取值。）








function makeProperty(o, name, predicate) {


    var value;  // This is the property value





    // The setter method simply returns the value.


    o["get" + name] = function() { return value; };





    // The getter method stores the value or throws an exception if


    // the predicate rejects the value.


    o["set" + name] = function(v) {


        if (predicate && !predicate(v))


            throw "set" + name + ": invalid value " + v;


        else


            value = v;


    };


}






// The following code demonstrates the makeProperty() method.



var o = {};  // Here is an empty object





// Add property accessor methods getName and setName()



// Ensure that only string values are allowed



makeProperty(o, "Name", function(x) { return typeof x == "string"; });



注意：predicate为函数指针。由于predicate定义为


function(x)


{


  return typeof x== "string";


}


需写成predicate(参数)来调用;








o.setName("Frank");  // Set the property value


print(o.getName());  // Get the property value


o.setName(0);        // Try to set a value of the wrong type