Javascript: Type Error vs Reference Error

In order to understand Type Error vs Reference Error, first we will need to know Variable Declaration vs Variable Initialization.

var x;

In this above statement, we can say that x is declared but not yet initialized.

var x = 5;

Here, we can say that x is declared and as well initialized.

Now, let’s say we would want to access the x’s property that has been declared but not initialized.

var x;
console.log(x);

This would result variable x to be

undefined

Now, let’s say that we would want to declare and initialize x to undefined and then access the x’s toString() method.

var x = undefined;
console.log(x.toString());

This would result in

Uncaught TypeError: Cannot read property ‘toString’ of undefined(…)

Now, let’s say we would like to access the x’s property thats been been declared as well as initialized.

var x = 5;
console.log(x.toString());

This would result

5   // Since 5 is declared and initialized as a number, 
    //and we were trying to convert it to a String.

Now, let’s say we would want to access a variable y that doesn’t exist in the scope (meaning that there is not presence of variable y with out any initialization or declaration)

console.log(y);

This would result in

Uncaught ReferenceError: y is not defined(…)

 

Happy Learning 🙂