How to fix the alert is not defined error in Node.js

In this tutorial, we are going to learn about how to fix The “ReferenceError: alert is not defined” in Node.js.

When we use a alert() method in the Node.js app to print something on the webpage, we will see the following error in the node.js command line.

Here is an example, of how we get the error:

const a = 12;
alert(a);

Output:

"ReferenceError: alert is not defined"

This error occurs because we are using the ‘alert()’ method in the server side Node.js environment.

But the alert() is only available in the browser environment, like mostly in front end code we can use that method.

To fix the ‘alert’ is not defined error, we can use console.log() method in place of alert() method.

const a = 12;
console.log(a);

We can also check if we are in the browser environment or server side by using the window object in Node.js.

Here is an example:

if(typeof window === "undefined"){
    console.log("Server side");
}else{
    console.log("Browser environment");
}