JavaScript:继承和常量声明 [英] JavaScript: Inheritance and Constant declaration

问题描述

帮助，我有这堂课

var jMath = {

    pi2: Math.PI,

    foo: function() {
        return this.pi2;
    }
}

我想使pi2不变，我想让jMath从Math对象继承.我该怎么办?

I want to make the pi2 constant and i want jMath to inherit from Math object. How do I do that?

推荐答案

哦，好笑的东西，从头开始，这是正确的版本:

Oh amusing, scratch all that, this is the correct version:

function JMath() {
   this.foo = function() {
        return this.PI;
    }
}

JMath.prototype = Math;

var jMath = new JMath();
alert(jMath.foo());

(与此处的其他答案匹配)

(which matches what the other answer is here)

(我最初尝试使用"JMath.prototype = new Math()"设置原型，这是我在其他地方看到的方式，但是上面的方法有效)

(I originally tried to set the prototype using "JMath.prototype = new Math()" which is how I've seen it other places, but the above works)

这里是单例完成的一种方法

Here's one way to do it as a singleton

//  Execute an inline anon function to keep
//  symbols out of global scope
var jMath = (function()
{
    //  Define the JMath "class"
    function JMath() {
        this.foo = function() {
            return this.PI;
        }
    }

    JMath.prototype = Math;

    // return singleton
    return new JMath();
})();

//  test it
alert( jMath.PI );

//  prove that JMath no longer exists
alert( JMath );

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