JavaScript错误："；不是一个函数；

看起来“$smth不是一个函数”是JavaScript的一个非常常见的问题，但是在浏览了很多线程之后，我仍然无法理解是什么导致了我的情况

我有一个自定义对象，定义为：

function Scorm_API_12() {
var Initialized = false;

function LMSInitialize(param) {
    errorCode = "0";
    if (param == "") {
        if (!Initialized) {
            Initialized = true;
            errorCode = "0";
            return "true";
        } else {
            errorCode = "101";
        }
    } else {
        errorCode = "201";
    }
    return "false";
}

// some more functions, omitted.
}

var API = new Scorm_API_12();

然后，在另一个脚本中，我尝试以以下方式使用此API：

var API = null;

function ScormProcessInitialize(){
    var result;

    API = getAPI();

    if (API == null){
        alert("ERROR - Could not establish a connection with the API.");
        return;
    }

    // and here the dreaded error pops up
    result = API.LMSInitialize("");

    // more code, omitted
    initialized = true;
}

getAPI（）的内容如下所示：

var findAPITries = 0;

function findAPI(win)
{
   // Check to see if the window (win) contains the API
   // if the window (win) does not contain the API and
   // the window (win) has a parent window and the parent window
   // is not the same as the window (win)
   while ( (win.API == null) &&
           (win.parent != null) &&
           (win.parent != win) )
   {
      // increment the number of findAPITries
      findAPITries++;

      // Note: 7 is an arbitrary number, but should be more than sufficient
      if (findAPITries > 7)
      {
         alert("Error finding API -- too deeply nested.");
         return null;
      }

      // set the variable that represents the window being
      // being searched to be the parent of the current window
      // then search for the API again
      win = win.parent;
   }
   return win.API;
}

function getAPI()
{
   // start by looking for the API in the current window
   var theAPI = findAPI(window);

   // if the API is null (could not be found in the current window)
   // and the current window has an opener window
   if ( (theAPI == null) &&
        (window.opener != null) &&
        (typeof(window.opener) != "undefined") )
   {
      // try to find the API in the current window�s opener
      theAPI = findAPI(window.opener);
   }
   // if the API has not been found
   if (theAPI == null)
   {
      // Alert the user that the API Adapter could not be found
      alert("Unable to find an API adapter");
   }
   return theAPI;
}

function Scorm_API_12() {
var Initialized = false;

this.LMSInitialize = function(param) {
    errorCode = "0";
    if (param == "") {
        if (!Initialized) {
            Initialized = true;
            errorCode = "0";
            return "true";
        } else {
            errorCode = "101";
        }
    } else {
        errorCode = "201";
    }
    return "false";
}

// some more functions, omitted.
}

var API = new Scorm_API_12();

现在，可能找到了API，因为我没有收到“无法找到…”消息，代码继续尝试初始化它。但是firebug告诉我

API.LMSInitialize不是一个函数

，如果我尝试用

警报（Object.getOwnPropertyNames（API））调试它，它会给我一个空白警报

我缺少什么？
您的
LMSInitialize
函数在
Scorm\u API\u 12
函数中声明。因此，它只能在
Scorm_API_12
函数的作用域中看到

如果您想像
API.LMSInitialize（“”）那样使用此函数，请像下面这样声明
Scorm_API_12
函数：

var findAPITries = 0;

function findAPI(win)
{
   // Check to see if the window (win) contains the API
   // if the window (win) does not contain the API and
   // the window (win) has a parent window and the parent window
   // is not the same as the window (win)
   while ( (win.API == null) &&
           (win.parent != null) &&
           (win.parent != win) )
   {
      // increment the number of findAPITries
      findAPITries++;

      // Note: 7 is an arbitrary number, but should be more than sufficient
      if (findAPITries > 7)
      {
         alert("Error finding API -- too deeply nested.");
         return null;
      }

      // set the variable that represents the window being
      // being searched to be the parent of the current window
      // then search for the API again
      win = win.parent;
   }
   return win.API;
}

function getAPI()
{
   // start by looking for the API in the current window
   var theAPI = findAPI(window);

   // if the API is null (could not be found in the current window)
   // and the current window has an opener window
   if ( (theAPI == null) &&
        (window.opener != null) &&
        (typeof(window.opener) != "undefined") )
   {
      // try to find the API in the current window�s opener
      theAPI = findAPI(window.opener);
   }
   // if the API has not been found
   if (theAPI == null)
   {
      // Alert the user that the API Adapter could not be found
      alert("Unable to find an API adapter");
   }
   return theAPI;
}

function Scorm_API_12() {
var Initialized = false;

this.LMSInitialize = function(param) {
    errorCode = "0";
    if (param == "") {
        if (!Initialized) {
            Initialized = true;
            errorCode = "0";
            return "true";
        } else {
            errorCode = "101";
        }
    } else {
        errorCode = "201";
    }
    return "false";
}

// some more functions, omitted.
}

var API = new Scorm_API_12();

有关调试此类问题的更多通用建议，MDN有一篇好文章：

试图像函数一样调用一个值，但该值不可用
实际上是一个函数。有些代码希望您提供函数，但是
那没有发生

也许函数名中有输入错误？也许你就是这样的对象
调用上的方法没有此函数？例如
JavaScript对象没有映射函数，但是JavaScript数组对象
做

基本上，对象（js中的所有函数也是对象）并不存在于您认为它存在的地方。原因可能有很多，包括（不是一个广泛的列表）：


缺少脚本库
打字错误
该功能在您当前无权访问的范围内，例如：


var x=function（）{
var y=函数（）{
警报（'y'）；
}
};
//全局作用域无法访问y，因为它在x中已关闭且未公开
//y不是已触发的函数错误
x、 y（）我也遇到了这个错误。在我的例子中，根本原因是异步相关的（在代码库重构期间）：没有等待生成“nota function”函数所属对象的异步函数，随后调用该函数的尝试会抛出错误，示例如下：

const car = carFactory.getCar();
car.drive() //throws TypeError: drive is not a function

解决办法是：

const car = await carFactory.getCar();
car.drive()

发布此消息有助于其他任何面临此错误的人。
我在使用JSON.parse和JSON.stringify（）复制类对象时收到此错误，该函数删除了以下函数：

class Rectangle {
  constructor(height, width) {
    this.height = height;
    this.width = width;
  }
  // Method
  calcArea() {
    return this.height * this.width;
  }
}

const square = new Rectangle(10, 10);

console.log('area of square: ', square.calcArea());

const squareCopy = JSON.parse(JSON.stringify(square));

// Will throw an exception since calcArea() is no longer function 
console.log('area of square copy: ', squareCopy.calcArea());

除了上面流行的答案之外，如果您正在使用服务或助手功能文件，并对稍后将在项目中导入的功能执行
导出

确保要导入的函数名与从服务、帮助程序或utils文件导出的函数的确切名称匹配，并且该函数实际存在于正确的文件中！我被这个错误缠住了，调试了几个小时，直到我发现这个错误才有所进展。
当你在
API=getAPI（）之后执行
console.log（API）
时，你会得到什么？请告诉我初始化后要执行的操作。我遇到了这个错误，因为我有一个循环依赖项。也许这会对其他人有所帮助。我想补充一点：将局部变量命名为函数，因此当调用
showOrderForm（）
时，
showOrderForm
的类型是布尔值。