Question

这是我第一次尝试javascript原型设计。我使用Espruino（微控制器的javascript解释器）从环境传感器获取数据。我试图暂停我的代码1000ms，然后执行getSensorReading（）方法，这是（我认为）位于另一个方法内部。如何执行getSensorReading（）方法？我认为这个错误是由此引起的：

setTimeout(function (e) { this.getSensorReading(); }, w); //Attempting to execute getSensorReading()

我收到此错误：

Uncaught Error: Function "getSensorReading" not found!  at line 1 col 8 { this.getSensorReading(); }
        ^ in function called from system

代码：

I2C1.setup({scl:b6, sda:b7});

function Sensor (theType, theAddress) {
  this.type = theType;   //i.e. PH
  this.address = theAddress;  //i2c Address
  this.sensorResult = 0; //Store sensor result
  this.cmdTable = {
    "Calibrate" : {  //List of Calibration commands and timeout value.
      "clear" : { "cmd" : "Cal,Clear",      "wait" : 300  },
      "mid"   : { "cmd" : "Cal,mid,7.00",   "wait" : 1300 },
      "low"   : { "cmd" : "Cal,low,4.00",   "wait" : 1300 },
      "high"  : { "cmd" : "Cal,high,10.00", "wait" : 1300 },
      "query" : { "cmd" : "Cal,?",          "wait" : 300  }
    },
    "Information" : {  //Device Information

    },
    "LED" : {  //Enable / Disable or Query the LEDs
      "L0" : { "cmd" : "L,0", "wait" : 300 },
      "L1" : { "cmd" : "L,1", "wait" : 300 },
      "L?" : { "cmd" : "L,?", "wait" : 300 }
    },
    "Reading" : {  //Takes a single reading
      "R" : { "cmd" : "R,25.6", "wait" : 1000 } //Takes a single temperature compensated reading
    },
    "Serial"      : {  //Switch back to UART mode

    },
    "Sleep"       : {  //Enter low power sleep mode

    },
    "Status"      : {  //Retrieve status information

    },
    "Temperature" : {  //Set or Query the temperature compensation
      "T"  : { "cmd" : "T,19.5", "wait" : 300 },  //Where the temperature is any value; floating point, or int, in ASCII form
      "T?" : { "cmd" : "T,?",   "wait" : 300 }  //Query the set temerature
    },
    "Factory"     : {  //Factory reset

    },
  };
}

Sensor.prototype = {
  constructor: Sensor,
  getSensorType:function () {
    return this.type; //Get Sensor type
  },
  getSensorAddress:function () {
    return this.address; //Get Sensor address
  },
  getSensorReading:function() {
    a = this.getSensorAddress;
    console.log("i2c Address: " + a);
    //d = I2C1.readFrom(a, 7);
    return d;
  },
  getSensorResult:function () {
    a = this.getSensorAddress;
    c = this.cmdTable.Reading.R.cmd;
    w = this.cmdTable.Reading.R.wait;

    //I2C1.writeTo(a, c);
    setTimeout(function (e) { this.getSensorReading(); }, w); //Attempting to execute getSensorReading()
  },
  storeSensorResult:function () {

  },
  updateResTemp:function (temp) {
    console.log("Before: " + this.cmdTable.Reading.R.cmd);
    this.cmdTable.Reading.R.cmd = "R," + temp;
    console.log("After: " + this.cmdTable.Reading.R.cmd);
  }
};

var ph = new Sensor("ph", 0x63);

ph.updateResTemp(90.5);
ph.getSensorResult();

Answer 1

在您的代码中，setTimeout回调中的“this”指的是父函数getSensorResult。该函数没有名为getSensorReading的函数。这就是错误的原因......另外，当您在函数内部使用全局变量时，可能会因为价格过高而导致变量。使用var关键字将其设为全球。尝试改变这样..

getSensorReading:function() {
    var a = this.getSensorAddress;
    console.log("i2c Address: " + a);
    //var d = I2C1.readFrom(a, 7);
    return d;
  },
getSensorResult:function () {
    var a = this.getSensorAddress;
    var c = this.cmdTable.Reading.R.cmd;
    var w = this.cmdTable.Reading.R.wait;
    var that = this;
    //I2C1.writeTo(a, c);
    setTimeout(function (e) { that.getSensorReading(); }, w); //Attempting to execute getSensorReading()
  }

Answer 2

声明全局方法foo和子方法bar并将子方法称为函数本身，您可以通过寻址先前声明的变量在子方法中使用this关键字，然后将return变量声明为子方法进程。

Foo: function()
{
    var a='a';
    var ret='b';

    var Bar = function()
    {
        this.a='a';
        return 'a';    
    }

    ret=Bar();

    return ret; 
}

Answer 3

同意调查this，Function.prototype.bind以及一般的原型链。此外，javascript是一种动态绑定语言。您可以重新绑定this。

您可以将对此的引用存储为闭包变量，也可以将传递给setTimeout的函数文字绑定到所需的上下文（Sensor.prototype或this in那个背景）

编辑：代替让bind可用，您可以通过应用，调用或关闭完成相同的操作。

getSensorResult:function () {
    a = this.getSensorAddress;
    c = this.cmdTable.Reading.R.cmd;
    w = this.cmdTable.Reading.R.wait;

    //I2C1.writeTo(a, c);
    setTimeout((function(_this) {
      return function (e) {
        _this.getSensorReading();
      }
    })(this), w); //Attempting to execute getSensorReading()
}

Javascript原型：如何在另一个方法中调用方法？

3 个答案: