Question

我是C＃中经验丰富的编码员，现在我已经处理过nodejs ..而且我无法按照我的预期让它工作：）

我有一个像这样声明的“类”：

var Gpio;

function Lights()
{
    [.more variables declared the same way..]
    this.o1 = "";
    this.o2 = "";
}

//then I have some methods added like this:
Lights.prototype.Init = function()
{
    var Gpio = require('pigpio').Gpio,
    //init of my variables
    o1 = new Gpio(17, {mode: Gpio.OUTPUT}),
    o2 = new Gpio(18, {mode: Gpio.OUTPUT});
}

//then I have other methods that try to use o1 and o2 
//that where already defined and initialiced

Lights.prototype.On = function(id)
{
    if(id == 1)
        o1.digitalWrite(true);
    else if(id == 2)
        o2.digitalWrite(true);
}

但是当我跑步时，我得到了：

o1.digitalWrite(false);
^

ReferenceError: o1 is not defined

如何通过这些方法制作那些o1 o2 o3可访问物？

Answer 1

与Java，C＃和其他语言不同，在JavaScript中， this关键字在访问实例变量时不可选。

您收到ReferenceError，因为当前范围内没有名为o1的变量。

尝试将其更改为：

Lights.prototype.On = function(id)
{
    if(id == 1)
        this.o1.digitalWrite(true);
    else if(id == 2)
        this.o2.digitalWrite(true);
}

（当然，您还需要更改Init方法）

作为最后一点，nodeJS支持ES6，其中包括class declarations - 它们使JS代码更整洁（更像是C＃），这可能对你有帮助。

以下是我为您的课程编写代码的方法：

const Gpio = require('pigpio').Gpio;

class Lights {
    constructor() {
        // there's no need to explicitly declare o1 and o2 here - they'll get 
        // created whenever they are assigned to. This is just for readability.
        this.o1 = null;
        this.o2 = null;
        // add any more properties here in the constructor - you can't
        // declare them in the class body like C#
        this.another = 5;
    }

    init() {
        // I'm assuming there's a reason you haven't done this in the constructor
        this.o1 = new Gpio(17, {mode: Gpio.OUTPUT}),
        this.o2 = new Gpio(18, {mode: Gpio.OUTPUT});
    }

    on(id) {
        // this assumes that init() has been called
        switch (id) {
          case 1: this.o1.digitalWrite(true); break;
          case 2: this.o2.digitalWrite(true); break;
        }
    }

    // methods can be static too
    static HELLO() {
       // you would call this method with Lights.HELLO()
       console.log('hello');
    }
}    

// if you need to access the Lights class from another nodejs source file, you'll
// need to export it (there's a few ways to do this, so read the docs)
exports.Lights = Lights;

// in main.js - import the Lights class and instantiate it
const Lights = require('./lights.js').Lights;
var light = new Lights();
light.init();
light.on(1);
// also note, there's no visibility restrictions in JS - all
//  properties and methods are public.
console.log(light.another);

如果您了解C＃，这应该很容易理解。

访问nodejs中的变量

1 个答案: