您如何在JavaScript中实现类似静态方法的功能？

Question

While I was looking through the documentation for String , referencing String.fromCharCode . I noticed that it was different from the majority of the other String methods in the way that it didn't have a .prototype before the method, Ex. String.prototype.CharCodeAt . I assume that it must be similar to that of a static reference in java given that it's usage requires you to reference the String class/Object, Ex.

var str = "foo";
var code = str.charCodeAt(0);
var character = String.fromCharCode(code); // This is the reference I'm talking about
alert(code); // Output: 102
alert(character); // Output: f

My question is how would you implement a method so that it is accessed in the same style as String.fromCharCode in your own code?

Answer 1

In JavaScript, functions are first-class objects. It makes it possible to assign method property directly to it, which would behave as static method:

function MyObject() {}
MyObject.static = function() { ... }

Just like you would expect.

Answer 2

DZone's ref card provides a great reference for the Object-oriented javascript, I highly recommend it. The related paragraphs

There is no direct support for static members. Constructor functions are used to create static members. Static members can't be accessed with “this” keyword.

private static members

   function Factory(){}
    // public static method
    Factory.getType = function (){
      return “Object Factory”;
    };

    // public static field
    Factory.versionId = “F2.0”;
    Factory.prototype.test = function(){
      console.log(this.versionId); // undefined
      console.log(Factory.versionId); // F2.0
      console.log(Factory.getType()); // Object Factory
    }
    var factory = new Factory();
    factory.test();

public static members

var Book = (function () {
// private static field
    var numOfBooks = 0;
// private static method
    function checkIsbn(isbn) {
        if (isbn.length != 10 && isbn.length != 13)
            throw new Error(“isbn is not valid!”);
    }

    function Book(isbn, title) {
        checkIsbn(isbn);
        this.isbn = isbn;
        this.title = title;
        numOfBooks++;
        this.getNumOfBooks = function () {
            return numOfBooks;
        }
    }

    return Book;
})();
var firstBook = new Book(“0-943396-04-2”, “First Title”);
console.log(firstBook.title); // First Title
console.log(firstBook.getNumOfBooks()); // 1
var secondBook = new Book(“0-85131-041-9”, “Second Title”);
console.log(firstBook.title); // First Title
console.log(secondBook.title); // Second Title
console.log(firstBook.getNumOfBooks()); // 2
console.log(secondBook.getNumOfBooks()); // 2