When working with any programming language, there will be a phase where you would have to deal with annoying bugs and errors. JavaScript especially has many hidden bugs and errors waiting for the best time to erupt in production. Whether you’re doing local or remote debugging, knowing how to fix these common JavaScript bugs will make your life easier.

In this article, we’ll explore various common JavaScript problems and how to solve them.

Uncaught ReferenceError: ‘x’ is not defined

This is one of the most common JavaScript errors, and it usually happens when there is a non-existent variable referenced somewhere in the code.

The variable is either not declared well, or declared in the wrong scope.

Look at the code below:

console.log(foo) // Uncaught ReferenceError: 'foo' is not defined

It would throw Uncaught ReferenceError: ‘foo’ is not defined since we don’t have foo declared. This can be fixed by declaring the variable foo:

var foo = "foobar";

console.log(foo) // foobar

Another example is the code below:

function add() {
  var x = 5, y = 1;
  return x + y;
}
console.log(x); // Uncaught ReferenceError: x is not defined

The issue here is x is only available in the scope of add function and cannot be used outside that function. However, the add function can access any global variable and its local variable.

To fix it, you will need to declare variable x as global variable.

var x = 5, y = 1

function add() {
  return x + y;
}
console.log(x); // 5

There you go! It’s fixed.

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