Cannot read properties of undefined (reading ‘ɵmod’)

A common error message in JavaScript is “cannot read properties of undefined (reading ‘ɵmod’)”.
This error typically occurs when you are trying to access a property or method on an undefined or null value.

To understand this error better, let’s consider an example:

        
            var person;
            console.log(person.name); // Throws "cannot read properties of undefined"
        
    

In the above example, we have declared a variable “person” but have not assigned any value to it.
Hence, it is considered as undefined. When we try to access the “name” property of “person”, the error is thrown.

This error is quite common when working with asynchronous code or when a function expects an object or an array as a parameter, but receives undefined or null.

Here’s another example:

        
            function validateUser(user) {
                console.log(user.name); // Throws "cannot read properties of undefined"
            }
            
            var user = null; // or user = undefined;
            validateUser(user);
        
    

In this example, the function “validateUser” expects an object with a “name” property as a parameter.
However, we pass null or undefined as the argument, resulting in the error.

To fix this error, you need to make sure you are dealing with valid and defined values before accessing their properties or methods. This can be done by using conditional checks or default values.

        
            var person;
            if (person) {
                console.log(person.name);
            } else {
                console.log("Person is undefined or null");
            }
        
    

In the updated example above, we added a conditional check to verify if “person” is defined before accessing the “name” property.
This prevents the error from being thrown and allows us to handle the situation appropriately.