Javascript中的Call方法讨论

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简述:

讨论一下Javascript中 Call的用法


call 方法(版本5.5以上)  :

文档中描述:

调用一个对象的一个方法,以另一个对象替换当前对象。

Call([thisObj[,arg1[, arg2[,  [,.argN]]]]])

thisObj

可选项。将被用作当前对象的对象。

arg1, arg2,  , argN

可选项。将被传递方法参数序列。


测试特性:

1. Person类对象转换(我觉得是种实例化对象后, 继承的形式)

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>Test Call</title></head><body><script type="text/javascript">function Person(name){this.name = null;this.showName = function(){document.write(this.name);};this.Init = function(name){      this.name = name;      }      this.Init(name);  };var jeremy = new Person("Jeremy");jeremy.showName();document.write("<br>");var tom = new Object();Person.call(tom); //Person class do call()tom.name = "Tom";tom.showName();</script></body>

输出:


2. 用call方法替换this指针

在这段代码中, NameShowing 类中,showName() 方法,需要有this.name 参数,

所以用call方法,传入实例jeremy.name, 用新对象jeremy替代this指针

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>Test Call</title></head><body><script type="text/javascript">function NameShowing(){this.showName = function(){document.write(this.name);}}function Person(name){this.name = null;this.Init = function(name){      this.name = name;      }      this.Init(name);  };var nameShowing = new NameShowing();var jeremy = new Person("Jeremy")//replace the 'this' pointer by jeremy objectnameShowing.showName.call(jeremy);</script></body></html>

输出:



3. 用call(obj),实例obj继承方法

jeremy做为一个Person的实例, 缺少showName()方法, 从NameShowing类中使用call , jeremy继承了showName() 方法

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>Test Call</title></head><body><script type="text/javascript">function NameShowing(){this.showName = function(){document.write(this.name);}}function Person(name){this.name = null;this.Init = function(name){      this.name = name;      }      this.Init(name);  };var jeremy = new Person("Jeremy")//pass showName() method to jeremy objectNameShowing.call(jeremy);jeremy.showName();</script></body></html>

输出:


4 call实现带有构造函数的参数 传入

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>Test Call</title></head><body><script type="text/javascript">function Person(name, age){this.name = null;this.age = null;this.showPersonInfo = function(){document.write("Name: " + this.name + "<br>");document.write("Age: " + this.age + "<br>");};this.Init = function(){this.name = name;this.age = age;};this.Init();}var jeremy = new Object();Person.call(jeremy, "Jeremy", 20);jeremy.showPersonInfo();</script></body></html>

输出:



call函数原理分析:

从上面call方法使用中,发生了原先的this指针被新的对象替代的方法,而原先的参数也就赋给了新的对象

从网上资料看到,

直接说就是,使用apply实现了 新对象对this指针的替代

例如下面代码使用到了apply 方法:

function A(a){document.write(a);};function AA(a){A.apply(this, arguments);}AA("output in AA");

输出是:



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