Javascript 学习笔记

实现同样的工作: starting and stopping an animation，可以有5种不同的方式完成

 

方式一：
/* Start and stop animations using functions. */
function startAnimation() {
...
}
function stopAnimation() {
...
}

方式二：
/* Anim class. */
var Anim = function() {
...
};
Anim.prototype.start = function() {
...
};
Anim.prototype.stop = function() {
...
};
/* Usage. */
var myAnim = new Anim();
myAnim.start();
myAnim.stop();

方式三：
/* Anim class, with a slightly different syntax for declaring methods. */
var Anim = function() {
...
};
Anim.prototype = {
    start: function() {
    ...
    },
    stop: function() {
    ...
    }
};

方式四：
/* Add a method to the Function object that can be used to declare methods. */
Function.prototype.method = function(name, fn) {
    this.prototype[name] = fn;
};
/* Anim class, with methods created using a convenience method. */
var Anim = function() {
...
};
Anim.method('start', function() {
...
});
Anim.method('stop', function() {
...
});

方式五：支持链式添加
/* This version allows the calls to be chained. */
Function.prototype.method = function(name, fn) {
this.prototype[name] = fn;
return this;
};
/* Anim class, with methods created using a convenience method and chaining. */
var Anim = function() {
...
};
Anim.
method('start', function() {
...
}).
method('stop', function() {
...
});

弱类型语言,基本类型：booleans,numbers,strings(javascript和其他语言不通，他把integers和floats作为相同的类型参考)

javascript灵活可变的class(function)
function displayError(message) {
displayError.numTimesExecuted++;
alert(message);
};
displayError.numTimesExecuted = 0;
It also means you can modify classes after they have been defined and objects after they
have been instantiated:
/* Class Person. */
function Person(name, age) {
this.name = name;
this.age = age;
}
Person.prototype = {
getName: function() {
return this.name;
},
getAge: function() {
return this.age;
}
}
/* Instantiate the class. */
var alice = new Person('Alice', 93);
var bill = new Person('Bill', 30);
/* Modify the class. */
Person.prototype.getGreeting = function() {
return 'Hi ' + this.getName() + '!';
};
/* Modify a specific instance. */
alice.displayGreeting = function() {
alert(this.getGreeting());
}
=========================
JavaScript没有块级作用域，函数中声明的所有变量无论是在哪里声明的，在整个函数中都有意义。javascript的方法申明的参数个数可以和调用时不同（采用从左到有的匹配方式）

============================

实现接口：

// Interfaces.
var Composite = new Interface('Composite', ['add', 'remove', 'getChild']);
var FormItem = new Interface('FormItem', ['save']);
// CompositeForm class
var CompositeForm = function(id, method, action) { // implements Composite, FormItem
...
};
...
function addForm(formInstance) {
Interface.ensureImplements(formInstance, Composite, FormItem);
// This function will throw an error if a required method is not implemented,
// halting execution of the function.
// All code beneath this line will be executed only if the checks pass.
...
}

 

// 接口定义.
var Interface = function(name, methods) {
if(arguments.length != 2) {
throw new Error("Interface constructor called with " + arguments.length +
"arguments, but expected exactly 2.");
}
this.name = name;
this.methods = [];
for(var i = 0, len = methods.length; i < len; i++) {
if(typeof methods[i] !== 'string') {
throw new Error("Interface constructor expects method names to be "
+ "passed in as a string.");
}
this.methods.push(methods[i]);
}
};

//静态方法
Interface.ensureImplements = function(object) {
if(arguments.length < 2) {
throw new Error("Function Interface.ensureImplements called with " +
arguments.length + "arguments, but expected at least 2.");
}
for(var i = 1, len = arguments.length; i < len; i++) {
var interface = arguments[i];
if(interface.constructor !== Interface) {
throw new Error("Function Interface.ensureImplements expects arguments"
+ "two and above to be instances of Interface.");
}
for(var j = 0, methodsLen = interface.methods.length; j < methodsLen; j++) {
var method = interface.methods[j];
if(!object[method] || typeof object[method] !== 'function') {
throw new Error("Function Interface.ensureImplements: object "
+ "does not implement the " + interface.name
+ " interface. Method " + method + " was not found.");
}
}
}
};