JavaScript error: “is not a function”

It looks like "$smth is not a function" is a very common problem with JavaScript, yet after looking through quite a few threads I still cannot understand what is causing it in my case.

I have a custom object, defined as:

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();

Then in a different script I am trying to use this API in the following way:

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;
}

The getAPI() stuff, looks like this:

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;
}

Now, the API is probably found, because I do not get the "Unable to find..." message, the code proceeds to try to initialize it. But firebug tells me API.LMSInitialize is not a function, and if I try to debug it with alert(Object.getOwnPropertyNames(API));, it gives me a blank alert.

What am I missing?

Answers:

Answer

Your LMSInitialize function is declared inside Scorm_API_12 function. So it can be seen only in Scorm_API_12 function's scope.

If you want to use this function like API.LMSInitialize(""), declare Scorm_API_12 function like this:

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();
Answer

For more generic advice on debugging this kind of problem MDN have a good article TypeError: "x" is not a function:

It was attempted to call a value like a function, but the value is not actually a function. Some code expects you to provide a function, but that didn't happen.

Maybe there is a typo in the function name? Maybe the object you are calling the method on does not have this function? For example, JavaScript objects have no map function, but JavaScript Array object do.

Basically the object (all functions in js are also objects) does not exist where you think it does. This could be for numerous reasons including(not an extensive list):

  • Missing script library
  • Typo
  • The function is within a scope that you currently do not have access to, e.g.:

var x = function(){
   var y = function() {
      alert('fired y');
   }
};
    
//the global scope can't access y because it is closed over in x and not exposed
//y is not a function err triggered
x.y();

  • Your object/function does not have the function your calling:

var x = function(){
   var y = function() {
      alert('fired y');
   }
};
    
//z is not a function error (as above) triggered
x.z();

Answer

I also hit this error. In my case the root cause was async related (during a codebase refactor): An asynchronous function that builds the object to which the "not a function" function belongs was not awaited, and the subsequent attempt to invoke the function throws the error, example below:

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

The fix was:

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

Posting this incase it helps anyone else facing this error.

Answer

string.split() function does not mutate itself. It returns an array and leave itself as unchanged as string. Looks like you want to split your str into individual characters from this line of code str.split("") and process. So see this code below:

function pair(str) {

    var tokens = str.split("");
    for (var i = 0; i < tokens.length; i++){
        var subArray = [];
        switch (tokens[i]){
         case "G":
              subArray.push("G", "C");
               break;
         case "C":
              subArray.push("C", "G");
               break;
         case "A":
               subArray.push("A", "T");
       break;
         case "T":
               subArray.push("T", "A");
               break;
       }
       tokens.splice(i, 1, subArray);
  }
  return str; // Not sure if you intend to return original str or not
              // So please see my note below:
}

I'm not sure at the bottom part of your code whether you indeed want to return the string.

NOTE: If you want to append those characters in subArray back to str and return, you can do this:

return tokens.concat(subArray).join('');
Answer
str.splice(i, 1, subArray);

str is string.

.splice() method of Array

Check your logic ( or typo possible there should be subArray )

subArray.splice(i, 1, subArray);
Answer

String.prototype.split doesn't change the string into an array, it returns an array. So you can do this str = str.split('');

Your original function worked because you can access strings with [] as well.

Answer

prodTarget is not a function but an argument of the function. Try this:

prodTarget = parseToFloat(prodTarget);

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