Error: Evaluation failed: TypeError: Cannot read properties of undefined (reading ‘default’)

The infamous “TypeError: Cannot read properties of undefined (reading ‘default’)” error. You’ve probably seen it before, and it’s likely left you scratching your head, wondering what on earth is going on. Fear not, dear developer, for we’re about to embark on a journey to conquer this pesky error once and for all.

What’s causing the error?

Before we dive into the solutions, let’s take a step back and understand what’s causing this error in the first place. The “TypeError: Cannot read properties of undefined (reading ‘default’)” error typically occurs when your code is trying to access a property (in this case, ‘default’) on an undefined object.

const myObject = undefined;
console.log(myObject.default); // Boom! Error: Evaluation failed: TypeError: Cannot read properties of undefined (reading 'default')

In the example above, we’re trying to access the ‘default’ property on an undefined object, which results in the error. But why does this happen? There are a few common scenarios that can lead to this error:

• Undefined variables or properties: If a variable or property is undefined, attempting to access its properties will result in this error.
• : If an object is null or empty, it’s essentially undefined, and trying to access its properties will throw the same error.
• Incorrect imports or exports: When working with modules or importing/exporting functions, a mistake in the import/export process can lead to an undefined object, causing the error.
• Async operations gone wrong: If an async operation fails or returns undefined, your code might try to access properties on the resulting undefined object, causing the error.

Solutions and Workarounds

Now that we understand the causes, let’s explore some solutions and workarounds to get your code up and running again.

1. Check for undefined variables and properties

The simplest solution is to check if the variable or property is undefined before trying to access its properties. You can do this using a simple if statement:

const myObject = undefined;
if (myObject !== undefined) {
    console.log(myObject.default);
}

This approach is effective, but it can become tedious when dealing with multiple variables or properties.

2. Use the Optional Chaining Operator (?.)

Introduced in ECMAScript 2020, the Optional Chaining Operator (?.) allows you to read the value of a property located deep within a chain of connected objects without having to check that each reference in the chain is valid.

const myObject = undefined;
console.log(myObject?.default); // undefined, no error!

This operator returns undefined if any part of the chain is null or undefined, preventing the error.

3. Use the Nullish Coalescing Operator (??)

The Nullish Coalescing Operator (??) returns the first operand if it’s not null or undefined, and the second operand if it is. You can use this operator to provide a default value if the original value is undefined.

const myObject = undefined;
console.log(myObject?.default ?? 'default value'); // 'default value'

This approach ensures that your code doesn’t throw an error and provides a fallback value instead.

4. Review your imports and exports

If you’re experiencing this error when working with imports and exports, double-check that you’re importing and exporting correctly. Make sure the module exists, and the export/import syntax is correct.

// myModule.js
export default function myFunction() {
    // ...
}

// main.js
import myFunction from './myModule.js';
console.log(myFunction()); // should work correctly

5. Handle async operations correctly

When working with async operations, make sure to handle errors and undefined values properly. Use try-catch blocks or async/await syntax to handle potential errors:

async function myAsyncFunction() {
    try {
        const result = await someAsyncOperation();
        console.log(result.default); // handle result correctly
    } catch (error) {
        console.error(error);
    }
}

Best Practices to Avoid the Error

While the solutions above can help fix the error, it’s essential to follow best practices to avoid it in the first place.

1. Initialize variables and properties correctly: Make sure to initialize variables and properties with a default value or null to avoid undefined values.
2. Use type checking and validation: Implement type checking and validation to ensure that variables and properties have the expected types and values.
3. Check for null and undefined before accessing properties: Always check for null and undefined before accessing properties to avoid the error.
4. Use the Optional Chaining Operator (?.) and Nullish Coalescing Operator (??) liberally: These operators can help prevent the error and provide a more robust coding experience.
5. Test and debug your code thoroughly: Thoroughly test and debug your code to catch errors early on and avoid unexpected behavior.

Conclusion

The “TypeError: Cannot read properties of undefined (reading ‘default’)” error might seem daunting, but with a solid understanding of its causes and the solutions outlined above, you’ll be well-equipped to tackle it head-on. By following best practices and being mindful of the pitfalls, you can write more robust and error-free code.

Solution	Description
Check for undefined variables and properties	Use an if statement to check if a variable or property is undefined before accessing its properties.
Use the Optional Chaining Operator (?.)	Use the Optional Chaining Operator to read the value of a property located deep within a chain of connected objects without having to check that each reference in the chain is valid.
Use the Nullish Coalescing Operator (??)	Use the Nullish Coalescing Operator to provide a default value if the original value is undefined or null.
Review imports and exports	Double-check that imports and exports are correct to avoid errors related to undefined objects.
Handle async operations correctly	Use try-catch blocks or async/await syntax to handle potential errors and undefined values when working with async operations.

By following these solutions and best practices, you’ll be well on your way to conquering the “TypeError: Cannot read properties of undefined (reading ‘default’)” error and writing more robust, error-free code.

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