Javascript 對(duì)象的解釋
2024-05-06 14:16:41
供稿：網(wǎng)友
所有的構(gòu)造器都是對(duì)象，而并非所有的對(duì)象都是構(gòu)造器.每個(gè)構(gòu)造器都有一個(gè)用來實(shí)現(xiàn)原型繼承、共享屬性的Prototype屬性。對(duì)象通過new 表達(dá)式創(chuàng)建；比如，new String("A String") 創(chuàng)建了一個(gè)String對(duì)象。沒有通過new而直接調(diào)用構(gòu)造器將有返回值，返回的類型將取決于構(gòu)造器。例如String("A String")產(chǎn)生一個(gè)原始的類型的字符串而不是一個(gè)對(duì)象。
ECMAScript支持基于原型的繼承。每個(gè)構(gòu)造器都有一個(gè)與之關(guān)聯(lián)的原型，而且通過此構(gòu)造器創(chuàng)建的對(duì)象都有一個(gè)與構(gòu)造器原型關(guān)聯(lián)的隱式引用（稱為，對(duì)象的原型）。進(jìn)一步說，一個(gè)原型可能有一個(gè)對(duì)其原型的非空隱式引用……，這被稱為，原型鏈。當(dāng)一個(gè)引用指向?qū)ο蟮膶傩?，這個(gè)引用指向原型鏈中的第一個(gè)對(duì)象的以此為名的屬性。換句話說，第一次，這個(gè)直接關(guān)聯(lián)的對(duì)象，將為這個(gè)屬性被檢查。如果這個(gè)對(duì)象包含以此為名的屬性，這個(gè)屬性就是引用指向的屬性。如過這個(gè)對(duì)象不包含以此為名的屬性，那么這個(gè)對(duì)象的原型將會(huì)被繼續(xù)檢查……
原文：
Object
ECMAScript does not contain proper classes such as those in C++, Smalltalk, or Java, but rather,supports constructors which create objects by executing code that allocates storage for the objects and initialises all or part of them by assigning initial values to their properties. All constructors are objects,but not all objects are constructors. Each constructor has a Prototype property that is used to implement prototype-based inheritance and shared properties. Objects are created by using constructors in new expressions; for example, new String("A String") creates a new String object. Invoking a constructor without using new has consequences that depend on the constructor. For example,String("A String") produces a primitive string, not an object.
ECMAScript supports prototype-based inheritance. Every constructor has an associated prototype, and every object created by that constructor has an implicit reference to the prototype (called the object's prototype) associated with its constructor. Furthermore, a prototype may have a non-null implicit reference to its prototype, and so on; this is called the prototype chain. When a reference is made to a property in an object, that reference is to the property of that name in the first object in the prototype chain that contains a property of that name. In other words, first the object mentioned directly is examined for such a property; if that object contains the named property, that is the property to which the reference refers; if that object does not contain the named property, the prototype for that object is examined next; and so on.
