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How to Handle JavaScript Uncaught TypeError: “x” is Not a Function

How to Handle JavaScript Uncaught TypeError: “x” is Not a Function

The Javascript error TypeError: "x" is not a function occurs when there is an attempt to call a function on a value or object, which is not actually a function.

Error message:

TypeError: "x" is not a function

Error Type:

TypeError

What Causes TypeError: "x" is not a function

A TypeError: "x" is not a function in Javascript generally occurs in one of the following scenarios:

  • A typographical error in a function call.
  • Missing script library.
  • When a function is called on a property that is not actually a function.
  • A TypeError: "x" is not a function occurs when a function is called on an object that does not contain the called function.
  • When calling a built-in function that expects a callback function argument, which does not exist.
  • When the called function is within a scope that is not accessible

TypeError: "x" is not a function Examples

1. Typo

A typical scenario for the TypeError: "x" is not a function to occur is when there is a typo in the called function name:

var elem = document.getElementByID('ID');

Running the above code leads to the following Javascript error:

TypeError: document.getElementByID is not a function

The correct function name is getElementById():

var elem = document.getElementById('ID');

2. Object Does Not Contain Function

Another common cause for the TypeError: "x" is not a function is when a function is called an object that does not actually contain the function:

var foo = {
   bar: function() {
      console.log("bar called");
   }
};
foo.baz();

In the above example, the foo object contains a function bar(). However, the above code attempts to call the function baz(), which foo does not contain. Running the above code leads to the following Uncaught TypeError: "x" is not a function:

Uncaught TypeError: foo.baz is not a function

If the Javascript code is modified to call the correct function bar():

var foo = {
   bar: function() {
      console.log("bar called");
   }
};    
foo.bar();

The correct output is produced:

bar called

How to Fix Javascript TypeError: "x" is not a function

The TypeError: "x" is not a function can be fixed using the following suggestions:

  • Paying attention to detail in code and minimizing typos.
  • Importing the correct and relevant script libraries used in code.
  • Making sure the called property of an object is actually a function.
  • Making sure objects contain the called function to avoid TypeError: "x" is not a function.
  • Making sure functions passed in as callbacks do exist.
  • Making sure called functions are within the correct and accessible scope.

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