javascript
JavaScript基于对象编程
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JavaScript基于對象編程
1、JavaScript變量/函數聲明在代碼執行之前被解析，并且變量聲明優先級高于函數聲明。
代碼片段：
1 2 3 4 5 6 7 | var? ?flag =? ?'test'? ?in? ?window; if? ?(!flag){ ????? ?var? ?test = 1; } ? new? ?StringBuffer(? ?'test = '? ?).append(test).toString(); |
執行結果：
test?=?undefined2、JavaScript中的this關鍵字指向當前執行上下文對象。
代碼片段：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | var? ?_this =? ?this? ?; var? ?id; var? ?name; function? ?User(){ ????? ?id = 110; ????? ?this? ?.name =? ?'andy'? ?; ????? ?return? ?this? ?; } ? var? ?userOject =? ?new? ?User(); var? ?_new_id = id; var? ?_new_name = name; var? ?_obj_id = userOject.id; var? ?_obj_name = userOject.name; ? var? ?userFunc = User(); var? ?_id = id; var? ?_name = name; var? ?_func_id = userFunc.id; var? ?_func_name = userFunc.name; ? ? new? ?StringBuffer(? ?'_this = '? ?).append( _this ). append(? ?';userOject = '? ?).append(userOject ).append(? ?';_new_id = '? ?).append(_new_id).append(? ?';_new_name = '? ?).append(_new_name ). append(? ?';_obj_id = '? ?).append(_obj_id ).append(? ?';_obj_name = '? ?).append( _obj_name ). append(? ?';userFunc = '? ?).append(userFunc ).append(? ?';_id = '? ?).append(_id ).append(? ?';_name = '? ?).append(_name). append(? ?';_func_id = '? ?).append(_func_id ).append(? ?';_func_name = '? ?).append( _func_name).toString(); |
執行結果：
_this?=?[object?Window] userOject?=?[object?Object] _new_id?=?110 _new_name?=?undefined _obj_id?=?undefined _obj_name?=?andy userFunc?=?[object?Window] _id?=?110 _name?=?andy _func_id?=?110 _func_name?=?andy3、JavaScript中通過new關鍵字調用的函數才是構造函數。(在構造函數內部 - 也就是被調用的函數內 - this 指向新創建的對象 Object。)
代碼片段：
1 2 3 4 5 6 7 8 9 10 11 12 | function? ?User(userName){ ????? ?this? ?.userName = userName; ????? ?return? ?this? ?; } var? ?zhengwei = User(? ?'鄭偉'? ?); var? ?andy =? ?new? ?User(? ?'andy'? ?); ? new? ?StringBuffer(? ?'zhengwei.constructor = '? ?).append(zhengwei.constructor). append(? ?';zhengwei instanceof User ='? ?).append((zhengwei? ?instanceof? ?User)). append(? ?';andy.constructor = '? ?).append(andy.constructor). append(? ?';andy instanceof User = '? ?).append((andy? ?instanceof? ?User)).toString(); |
執行結果：
zhengwei.constructor?=?[object?Window] zhengwei?instanceof?User?=false andy.constructor?=?function?User(userName){this.userName?=?userNamereturn?this} andy?instanceof?User?=?true4、JavaScript中所有變量都是對象，除了兩個例外 null 和 undefined。
代碼片段：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | var? ?undefind_test =? ?'undefind'? ?in? ?window; var? ?null_test =? ?'null'? ?in? ?window; var? ?_undefind =? ?null? ?; ? var? ?undefind_toString; try? ?{ ????? ?undefind_toString = undefind.toString(); }? ?catch? ?(e){ ????? ?undefind_toString = e; } ? var? ?null_toString; try? ?{ ????? ?null_toString =? ?null? ?.toString(); }? ?catch? ?(e){ ????? ?null_toString = e; } ? var? ?boolean_toString =? ?false? ?.toString(); var? ?number_toString = (2..toString() || 2 .toString() || (2).toString()); var? ?array_toString = [1,2,3].toString(); ? new? ?StringBuffer(? ?'undefind_test = '? ?).append(undefind_test). append(? ?';null_test = '? ?).append( null_test). append(? ?';_undefind = '? ?).append(_undefind). append(? ?';undefind_toString = '? ?).append(undefind_toString). append(? ?';null_toString = '? ?).append(null_toString). append(? ?';boolean_toString = '? ?).append(boolean_toString). append(? ?';number_toString = '? ?).append(number_toString). append(? ?';array_toString = '? ?).append(array_toString).toString(); |
執行結果：
undefind_test?=?false null_test?=?false _undefind?=?null undefind_toString?=?ReferenceError:?undefind?is?not?defined null_toString?=?TypeError:?null?has?no?properties boolean_toString?=?false number_toString?=?2 array_toString?=?1,2,35、JavaScript的對象可以作為哈希表使用，主要用來保存命名的鍵與值的對應關系。使用對象的字面語法 - {} - 可以創建一個簡單對象。這個新創建的對象從 Object.prototype 繼承。
代碼片段：
1 2 3 4 5 6 7 8 9 10 | var? ?Person = {id :? ?'001'? ?, userName :? ?'鄭偉'? ?}; Person.age = 28; ? new? ?StringBuffer(? ?"Person = "? ?).append(Person). append(? ?";Person.constructor = "? ?).append(Person.constructor). append(? ?";(Person instanceof Object) = "? ?).append((Person? ?instanceof? ?Object)). append(? ?";Person['id'] = "? ?).append(Person[? ?'id'? ?]). append(? ?";Person.userName = "? ?).append(Person.userName). append(? ?";Person['age'] = "? ?).append(Person[? ?'age'? ?]).toString(); |
執行結果：
Person?=?[object?Object] Person.constructor?=?function?Object()?{[native?code] } (Person?instanceof?Object)?=?true Person['id']?=?001 Person.userName?=?鄭偉 Person['age']?=?286、JavaScript原型屬性。(基于原型模型實現繼承的對象最終形成原型鏈,新創建的對象的 prototype 被指向到構造函數的 prototype)
代碼片段：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 | var? ?Person =? ?function? ?(){}; Person.prototype =? ?new? ?Object(); // early binding -- Class template Person.prototype.id =? ?'001'? ?; Person.prototype.userName =? ?'鄭偉'? ?; Person.prototype.age = 28; Person.prototype.say =? ?function? ?(){ ????? ?return? ?"[id = "? ?+? ?this? ?.id +? ?", userName = "? ?+? ?this? ?.userName +? ?",age = "? ?+? ?this? ?.age +? ?"]"? ?; } ? var? ?person =? ?new? ?Person(); // later binding -- Instance template /*person.id = '001' person.userName = '鄭偉'; person.age = 28; person.say = function(){ ????? ?return "[id = " + this.id + ", userName = " + this.userName + ",age = " + this.age + "]"; }*/ var? ?_prototype_toString =? ?new? ?StringBuffer(); var? ?count = -1; for? ?(? ?var? ?n? ?in? ?Person.prototype) { ????? ?if? ?(count >= 0){ ????????? ?_prototype_toString.append(? ?","? ?); ????? ?} ????? ?_prototype_toString.append(n).append(? ?"="? ?).append(Person.prototype[n]); ????? ?count ++; } ? new? ?StringBuffer(? ?'Object.prototype = '? ?).append(Object.prototype). append(? ?';Object.constructor = '? ?).append(Object.constructor). append(? ?';Object.prototype.constructor = '? ?).append(Object.prototype.constructor). append(? ?';(person instanceof Object) = '? ?).append((Person? ?instanceof? ?Object)). append(? ?';person.constructor = '? ?).append(Person.constructor). append(? ?";person.say() = "? ?).append(person.say()). append(? ?";_prototype_toString = "? ?).append(_prototype_toString.toString()).toString(); |
執行結果：
Object.prototype?=?[object?Object] Object.constructor?=?function?Function()?{[native?code] } Object.prototype.constructor?=?function?Object()?{[native?code] } (person?instanceof?Object)?=?true person.constructor?=?function?Function()?{[native?code] } person.say()?=?[id?=?001,?userName?=?鄭偉,age?=?28] _prototype_toString?=?id=001,userName=鄭偉,age=28,say=function?(){return?"[id?=?"?+?this.id?+?",?userName?=?"?+?this.userName?+?",age?=?"?+?this.age?+?"]"}7、基于構造函數（對象冒充）實現JavaScript對象繼承。（支持多重繼承，不支持instanceof關鍵字，多層繼承時調用層次過多）
代碼片段：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 | // Define baseClass. function? ?BaseClass(id, name){ ????? ?this? ?.id = id; ????? ?this? ?.name = name; ????? ?this? ?.toString =? ?function? ?(){ ????????? ?return? ?'id = '? ?+? ?this? ?.id +? ?', name ='? ?+? ?this? ?.name; ????? ?}; } ? ? // Define subclass. function? ?SubClass(){ ????? ?BaseClass.apply(? ?this? ?, arguments); ????? ?this? ?.identifer = arguments[arguments.length - 1]; ????? ?this? ?.toString =? ?function? ?(){ ????????? ?return? ?BaseClass.prototype.toString.call(? ?this? ?) +? ?', identifer = '? ?+? ?this? ?.identifer; ????? ?}; } ? var? ?subClass =? ?new? ?SubClass(1,? ?'subClass'? ?,? ?'0001'? ?); ? new? ?StringBuffer(? ?'subClass.toString() = '? ?).append(subClass.toString()). append(? ?';subClass.constructor = '? ?).append(subClass.constructor). append(? ?';(subClass.constructor? === SubClass) = '? ?).append((subClass.constructor? === SubClass)). append(? ?';(subClass instanceof SubClass) = '? ?).append((subClass? ?instanceof? ?SubClass)). append(? ?';(subClass instanceof BaseClass) = '? ?).append((subClass? ?instanceof? ?BaseClass)).toString(); |
執行結果：
subClass.toString()?=?[object?Object],?identifer?=?0001 subClass.constructor?=?function?SubClass(){BaseClass.apply(this,?arguments)this.identifer?=?arguments[arguments.length?-?1]this.toString?=?function(){return?BaseClass.prototype.toString.call(this)?+?',?identifer?=?'?+?this.identifer}} (subClass.constructor??===?SubClass)?=?true (subClass?instanceof?SubClass)?=?true (subClass?instanceof?BaseClass)?=?false8、基于原型（代碼模板）實現JavaScript對象繼承。（不支持多重繼承，支持instanceof關鍵字，多層繼承時模版復用）
代碼片段：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 | // Define baseClass function? ?BaseClass(){} BaseClass.prototype.id =? ?null? ?; BaseClass.prototype.name =? ?null? ?; BaseClass.prototype.toString =? ?function? ?(){ ????? ?return? ?'id = '? ?+? ?this? ?.id +? ?', name ='? ?+? ?this? ?.name; }; ? ? // Define subClass function? ?SubClass(){} SubClass.prototype =? ?new? ?BaseClass(); ? SubClass.prototype.identifer =? ?null? ?; SubClass.prototype.toString =? ?function? ?(){ ????? ?return? ?BaseClass.prototype.toString.call(? ?this? ?) +? ?', identifer = '? ?+? ?this? ?.identifer; }; ? // The subclass is instanced. var? ?subClass =? ?new? ?SubClass(); subClass.id = 1; subClass.name =? ?'subClass'? ?; subClass.identifer =? ?'0001'? ?; ? // Output new? ?StringBuffer(? ?'subClass.toString() = '? ?).append(subClass.toString()). append(? ?';subClass.constructor = '? ?).append(subClass.constructor). append(? ?';(subClass.constructor? === SubClass) ='? ?).append((subClass.constructor? === SubClass)). append(? ?';(subClass instanceof SubClass) = '? ?).append((subClass? ?instanceof? ?SubClass)). append(? ?';(subClass instanceof BaseClass) = '? ?).append((subClass? ?instanceof? ?BaseClass)).toString(); |
執行結果：
subClass.toString()?=?id?=?1,?name?=subClass,?identifer?=?0001 subClass.constructor?=?function?BaseClass(){} (subClass.constructor??===?SubClass)?=false (subClass?instanceof?SubClass)?=?true (subClass?instanceof?BaseClass)?=?true9、基于 構造函數（封裝類屬性-成員變量） + 原型 （封裝類行為-方法）實現JavaScript對象繼承。（不支持多重繼承，支持instanceof關鍵字，多層繼承時模版復用）
代碼片段：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 | // Define baseclass. function? ?BaseClass(id, name){ ????? ?this? ?.id = id; ????? ?this? ?.name = name; } // Overwrite toString method. BaseClass.prototype.toString =? ?function? ?(){ ????? ?return? ?'id = '? ?+? ?this? ?.id +? ?', name ='? ?+? ?this? ?.name; }; ????? ? // Define subclass. function? ?SubClass(){ ????? ?BaseClass.apply(? ?this? ?, arguments); ????? ?this? ?.identifer = arguments[arguments.length - 1]; } // Subclass extends base class. SubClass.prototype =? ?new? ?BaseClass(); SubClass.prototype.constructor = SubClass; SubClass.prototype.toString =? ?function? ?(){ ????? ?return? ?BaseClass.prototype.toString.call(? ?this? ?) +? ?', identifer = '? ?+? ?this? ?.identifer; }; ????????? // The subclass is intanced. var? ?subClass =? ?new? ?SubClass(1,? ?'subClass'? ?,? ?'0001'? ?); ? // Output new? ?StringBuffer(? ?'subClass.toString() = '? ?).append(subClass.toString()). append(? ?';subClass.constructor = '? ?).append(subClass.constructor). append(? ?';(subClass.constructor? === SubClass) ='? ?).append((subClass.constructor? === SubClass)). append(? ?';(subClass instanceof SubClass) = '? ?).append((subClass? ?instanceof? ?SubClass)). append(? ?';(subClass instanceof BaseClass) = '? ?).append((subClass? ?instanceof? ?BaseClass)).toString(); |
執行結果：
subClass.toString()?=?id?=?1,?name?=subClass,?identifer?=?0001 subClass.constructor?=?function?SubClass(){BaseClass.apply(this,?arguments)this.identifer?=?arguments[arguments.length?-?1]} (subClass.constructor??===?SubClass)?=true (subClass?instanceof?SubClass)?=?true (subClass?instanceof?BaseClass)?=?true10、基于 對象結構（哈希表key-value）實現JavaScript對象繼承。（支持多重繼承，不支持instanceof關鍵字，多層繼承時模版迭代）
代碼片段：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 | // Define class factory. var? ?ClassFactory = { ????? ?createClass :? ?function? ?(){ ????????? ?// To defind the current constructor. ????????? ?var? ?CurrentClass =? ?function? ?(){}; ????????? ?// Agreed the final parameter for the current class extends the prototype, for the rest of the parameters so as to realize the parent class. ????????? ?var? ?extendsPrototype = arguments[arguments.length - 1] || {}; ????????? ?for? ?(? ?var? ?i? ?in? ?arguments){ ????????????? ?if? ?(i == arguments.length - 1)? ?break? ?; ????????????? ?var? ?superClass = arguments[i]; ????????????? ?var? ?ordinal = superClass.ORDINAL = i; ????????????? ?if? ?(? ?'function'? ?===? ?typeof? ?(superClass)){ ????????????????? ?superClass = superClass.prototype; ????????????? ?} ????????????? ?var? ?superPrototype = extendsPrototype[ordinal] = {}; ????????????? ?for? ?(? ?var? ?key? ?in? ?superClass) { ????????????????? ?// Determine whether the current members of the current class ????????????????? ?if? ?(superClass.hasOwnProperty(key)){ ????????????????????? ?superPrototype[key] = superClass[key]; ????????????????? ?}? ?else? ?{ ????????????????????? ?extendsPrototype[key] = superClass[key]; ????????????????? ?} ????????????? ?} ????????? ?} ????????? ????????? ?// Prototype will expand after the prototype chain of pointing to the current class. ????????? ?CurrentClass.prototype = extendsPrototype; ????????? ?CurrentClass.prototype.constructor = CurrentClass; ????????? ?return? ?CurrentClass; ????? ?} }; // Define class A var? ?A = ClassFactory.createClass({ ????? ?width : 100, ????? ?getWidth :? ?function? ?(){ ????????? ?return? ?this? ?.width; ????? ?} }); ? // Define class B var? ?B = ClassFactory.createClass({ ????? ?width : 200, ????? ?height : 100, ????? ?getWidth :? ?function? ?(){ ????????? ?return? ?this? ?.width; ????? ?}, ????? ?getHeight :? ?function? ?(){ ????????? ?return? ?this? ?.height; ????? ?} }); ? // Define class C var? ?C = ClassFactory.createClass(A, B,{ ????? ?width : 300, ????? ?getWidth :? ?function? ?(){ ????????? ?return? ?this? ?.width; ????? ?} }); ? // Initialize C object var? ?c =? ?new? ?C(); ? // Output new? ?StringBuffer(? ?'c.constructor = '? ?).append(c.constructor). append(? ?';(c.constructor === C) = '? ?).append((c.constructor === C)). append(? ?';(c instanceof C) = '? ?).append((c? ?instanceof? ?C)). append(? ?';((c instanceof A) || (c instanceof B)) = '? ?).append(((c? ?instanceof? ?A) || (c? ?instanceof? ?B))). append(? ?';c.getWidth() = '? ?).append(c.getWidth()). append(? ?';c[A.ORDINAL].getWidth() = '? ?).append(? ?(c[A.ORDINAL]).getWidth()? ?). append(? ?';c[B.ORDINAL].getWidth() = '? ?).append(? ?(c[B.ORDINAL]).getWidth()? ?). append(? ?';c[B.ORDINAL].getHeight() = '? ?).append(? ?(c[B.ORDINAL]).getHeight()? ?).toString(); |
執行結果：
c.constructor?=?function?(){} (c.constructor?===?C)?=?true (c?instanceof?C)?=?true ((c?instanceof?A)?||?(c?instanceof?B))?=?false c.getWidth()?=?300 c[A.ORDINAL].getWidth()?=?100 c[B.ORDINAL].getWidth()?=?200 c[B.ORDINAL].getHeight()?=?10011、基于 構造函數（封裝類屬性-成員變量） + 原型 （封裝類行為-方法）實現JavaScript對象繼承推薦寫法。（不支持多重繼承，支持instanceof關鍵字，多層繼承時模版復用）
代碼片段：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 | // Define class factory. var? ?ClassFactory = { ????? ?createClass :? ?function? ?(){ ????????? ?// To defind the current constructor. ????????? ?// TODO set member Variables ????????? ?var? ?CurrentClass =? ?function? ?(){ ????????????? ?if? ?(? ?this? ?.initialize){ ????????????????? ?this? ?.initialize.apply(? ?this? ?, arguments); ????????????? ?} ????????? ?}; ????????? ?// The current class to extends base class. ????????? ?var? ?SuperClass = arguments[0] ||? ?''? ?; ????????? ?if? ?(? ?typeof? ?(SuperClass) ===? ?'function'? ?){ ????????????? ?CurrentClass.prototype =? ?new? ?SuperClass(); ????????? ?}? ?else? ?{ ????????????? ?// If current class is base class, then current class prototype direct at Object prototype. ????????????? ?CurrentClass.prototype =? ?new? ?Object(); ????????? ?} ????????? ?CurrentClass.prototype.constructor = CurrentClass; ????????? ????????? ?// The current class to extend prototype. ????????? ?var? ?extendsPrototype = arguments[arguments.length - 1] || {}; ????????? ?for? ?(? ?var? ?key? ?in? ?extendsPrototype){ ????????????? ?CurrentClass.prototype[key] = extendsPrototype[key]; ????????? ?} ????????? ????????? ?return? ?CurrentClass; ????? ?} } // Define base class. var? ?SuperComponent = ClassFactory.createClass({ ????? ?initialize :? ?function? ?(title, index){ ????????? ?this? ?.rootNodeName =? ?'js_oo'? ?; ????????? ?this? ?.className =? ?'demo_container'? ?; ????????? ?this? ?.title = title; ????????? ?this? ?.index = index; ????? ?}, ????? ?getScript :? ?function? ?(){ ????????? ?throw? ?new? ?Error(? ?'The method must be implemented sub class!'? ?); ????? ?} }); // Define sub class. var? ?TestComponent = ClassFactory.createClass(SuperComponent, { ????? ?getScript :? ?function? ?(){ ????????? ?var? ?_script =? ?new? ?StringBuffer(); ????????? ?_script.append(? ?this? ?.title); ????????? ?return? ?_script.toString(); ????? ?} }); ????? var? ?testComponent =? ?new? ?TestComponent(? ?"TestComponent"? ?, 2); ? // Output new? ?StringBuffer(? ?'testComponent.constructor = '? ?).append(testComponent.constructor). append(? ?';(testComponent.constructor === TestComponent) = '? ?).append((testComponent.constructor === TestComponent)). append(? ?';(testComponent instanceof? TestComponent) = '? ?).append((testComponent? ?instanceof? ? ?TestComponent)). append(? ?';(testComponent instanceof? SuperComponent) = '? ?).append((testComponent? ?instanceof? ? ?SuperComponent)). append(? ?';testComponent.getScript() = '? ?).append(testComponent.getScript()).toString(); |
執行結果：
testComponent.constructor?=?function?(){if(this.initialize){this.initialize.apply(this,?arguments)}} (testComponent.constructor?===?TestComponent)?=?true (testComponent?instanceof??TestComponent)?=?true (testComponent?instanceof??SuperComponent)?=?true testComponent.getScript()?=?TestComponent轉載于:https://my.oschina.net/andy0807/blog/190677
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