JavaScript Object Constructors

 

一個 JavaScript Object Constructor (Function Constructor) 範例如下

function Person(first, last, age, eye) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eye;
}

var myFather = new Person("John", "Doe", 50, "blue");
var myMother = new Person("Sally", "Rally", 48, "green");

console.log(myFather.firstName);
console.log(myMother.firstName);

Function Constructor 利用 this 這關鍵字來建構自己的屬性，

Function Constructor 是一個 object，而你在使用時會覺得 Person 像是個 class。

 

你可以在已宣告的變數 myFather 或 myMother 添加額外屬性

function Person(first, last, age, eye) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eye;
}

var myFather = new Person("John", "Doe", 50, "blue");
var myMother = new Person("Sally", "Rally", 48, "green");

console.log(myFather.firstName);
console.log(myMother.firstName);

myFather.nationality = "English";
console.log(myFather.nationality);

 

但不可以在 Person 的 Constructor 以下面方式添加額外屬性，雖然不會報錯，

但 myFather 或 myMother 物件也不會有 nationality 屬性

function Person(first, last, age, eye) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eye;
}

var myFather = new Person("John", "Doe", 50, "blue");
var myMother = new Person("Sally", "Rally", 48, "green");

console.log(myFather.firstName);
console.log(myMother.firstName);

Person.nationality = "English";
console.log(myFather.nationality);

 

JavaScript 內建了以下 Constructors

var x1 = new Object();   // A new Object object
var x2 = new String();   // A new String object
var x3 = new Number();   // A new Number object
var x4 = new Boolean();  // A new Boolean object
var x5 = new Array();    // A new Array object
var x6 = new RegExp();   // A new RegExp object
var x7 = new Function(); // A new Function object
var x8 = new Date();     // A new Date object

console.log(typeof x1);
console.log(typeof x2);
console.log(typeof x3);
console.log(typeof x4);
console.log(typeof x5);
console.log(typeof x6);
console.log(typeof x7);
console.log(typeof x8);

 

但在大部份情況，則不需要用 object 這麼複雜的作法來處理，使用以下方式更為直覺快速

var x1 = {};            // new object
var x2 = "";            // new primitive string
var x3 = 0;             // new primitive number
var x4 = false;         // new primitive boolean
var x5 = [];            // new array object
var x6 = /()/           // new regexp object
var x7 = function () { };  // new function object

console.log(typeof x1);
console.log(typeof x2);
console.log(typeof x3);
console.log(typeof x4);
console.log(typeof x5);
console.log(typeof x6);
console.log(typeof x7);