TypeError: JavaScript

Can you add a number and a letter together?

If I ask you to give me the result of the addition of 1 plus H will you be able to give me the answer?

The obvious answer is NO.

The same goes in JavaScript! If you add 1 and H in JavaScript or when you try to perform operations on two operands of unmatched types, JavaScript throws a TypeError.

Per MDN: ‘A TypeError is thrown when an operand or argument passed to a function is incompatible with the type expected by that operator or function.’

Therefore, it becomes necessary to make sure the variables must have the same data types before performing any operation. Type mismatch generates an error while executing the whole program.

Types of TypeErrors

For example, you will get Uncaught TypeError if you are trying to convert a number to an uppercase character. As toUpperCase() is a function to convert a string to uppercase characters, it will throw an error for following code structure.

Code structure

var num=1;
try{
num.toUpperCase();
} 
catch(err){     
document.getElementById("demo").innerHTML = err.name;
}

Error

How to Get Rid of This Uncaught Type Error: Cannot Set a Property

There are many methods possible to overcome this error.

1. Using the toString() Function

You can use the toString() function to convert a number into a string first and then you can convert that string to upper case characters using the toUpperCase() function.

var num = 1; 
try {       
num.toString().toUpperCase();   // Convert number into string first 
}
catch(err) {    
document.getElementById("demo").innerHTML = err.name; 
}

Output

"1"

2. Using Constructor New String() of a Predefined Class

var num = 1; 
num=new String(num);
try {   
num.toUpperCase();   // You cannot convert a number to upper case 
}
catch(err){     
document.getElementById("demo").innerHTML = err.name; 
}

Output

"1"

Here are few more TypeErrors that can be thrown by JavaScript in different browsers.

TypeError Related to console.log()

TypeError: Property 'log' of object # is not a function (Chrome)
TypeError: console.log is not a function (Firefox) 
TypeError: 'your string' is not a function (evaluating 'console.log("your string")') (Safari)
TypeError: Function expected (IE)

TypeError Related to prompt()

TypeError: Property 'prompt' of object [object Object] is not a function (Chrome) 
TypeError: prompt is not a function (Firefox) 
TypeError: 'a string, this could vary' is not a function (evaluating 'prompt("your question")') (Safari)
TypeError: Function expected (IE)

TypeError Related to confirm()

TypeError: Property 'confirm' of object [object Object] is not a function (Chrome)
TypeError: confirm is not a function (Firefox)
TypeError: 'a string, this could vary' is not a function (evaluating 'confirm("your question")') (Safari)
TypeError: Function expected (IE)