Closures Development Tutorials, Guides & Insights

Creating custom error classes allows you to define specific error types that can provide more meaningful context when something goes wrong.

class ValidationError extends Error {
    constructor(message) {
        super(message);
        this.name = 'ValidationError';
    }
}

function validateInput(input) {
    if (input === '') {
        throw new ValidationError('Input cannot be empty.');
    }
}

try {
    validateInput('');
} catch (error) {
    if (error instanceof ValidationError) {
        console.error(`Validation error: ${error.message}`);
    } else {
        console.error(`Unknown error: ${error.message}`);
    }
}

function counter() {
    let count = 0;

    return function() {
        count++;
        console.log(count);
    };
}

const increment = counter();
increment();  // Output: 1
increment();  // Output: 2
increment();  // Output: 3

In this example, the count variable is private to the counter function. The only way to manipulate count is through the returned function, which forms a closure over the count variable.