How to Throw an Error in JavaScript

An essential aspect of robust programming development is the method of managing errors. Throwing errors serves as a mechanism to address and react to unforeseen circumstances within your JavaScript code. Programmers who are adept at throwing errors can create code that is easier to utilize and maintain.

Why Throw Errors?

Throwing errors enables you to do the following:

• ✅ You can stop your code's standard execution and let others know that something startling occurred by raising an error.
• ✅ An error message that makes sense of what turned out badly or code gone wrong can be incorporated when an error is thrown.
• ✅ You might guarantee that your application can come up short or work effortlessly by utilizing try...catch blocks to catch the thrown errors and treat them.

The Statement for Throwing Error: throw

In JavaScript, you can generate an error by using the throw statement. The syntax is quite straightforward:

throw expression;

Throwing a Basic Error

Here is a basic representation of a basic error:

throw new Error("Something went wrong!");

In this illustration, an instance of an Error object is created, subsequently thrown, and contains the message "Something went wrong!"

Utilizing Custom Error Types

Albeit the most successive error type to throw in JavaScript is an Error object, there are various other underlying error types that may be useful for more specific error handling:

• ✅ Type Error
• ✅ Syntax Error
• ✅ Reference Error
• ✅ Range Error
• ✅ URI Error

For example:

By subclassing the Error class, you can create unique types of errors that are quite intriguing:

throw new TypeError("This is a type error!");

Conditionally Throwing Errors

In certain situations, error messages are typically generated when specific conditions are met. For instance, consider the example provided below:

function divide(a, b) {
    if (b === 0) {
        throw new Error("Cannot divide by zero!");
    }
    return a / b;
}

try {
    console.log(divide(4, 2)); 
    console.log(divide(4, 0)); // Throws an error
} catch (error) {
    console.error(error.message); 
}

Output:

2
Cannot divide by zero!

In this scenario, attempting to isolate by zero results in the divide function generating an error. This problem is detected by the try...catch construct, which subsequently records the error message to the control center.

Error Propagation

As you move up the call stack, exceptions can propagate until they are intercepted by an error handler. To conceptualize this, consider the following outline:

function functionA() {
    functionB();
}

function functionB() {
    throw new Error("Error in functionB");
}

try {
    functionA();
} catch (error) {
    console.error(error.message); 
}

Output:

Error in functionB

In this scenario, an error raised within function B is propagated back to function A, where it is intercepted by the try...catch statement present in that function.

Try, catch, finally keywords

The concluding block can be bypassed; it executes regardless of whether an error has occurred. This is advantageous for releasing resources or finalizing tasks that must be accomplished irrespective of an error situation.

try {
    throw new Error("Something went wrong");
} catch (error) {
    console.error(error.message); 
} finally {
    console.log("This will always run"); 
}

Output:

Something went wrong
This will always run

Example:

Let’s examine a sample code that demonstrates different kinds of errors and the methods to manage them effectively.

class CustomError extends Error {
    constructor(message) {
        super(message);
        this.name = "CustomError";
    }
}

function demoErrors(type) {
    switch (type) {
        case 'generic':
            throw new Error("This is a generic error!");
        case 'type':
            throw new TypeError("This is a type error!");
        case 'range':
            throw new RangeError("This is a range error!");
        case 'custom':
            throw new CustomError("This is a custom error!");
        default:
            console.log("No error thrown.");
    }
}

const errorTypes = ['generic', 'type', 'range', 'custom', 'none'];

errorTypes.forEach(type => {
    try {
        console.log(`\nThrowing ${type} error:`);
        demoErrors(type);
    } catch (error) {
        if (error instanceof CustomError) {
            console.error(`Caught a custom error: ${error.name} - ${error.message}`);
        } else if (error instanceof TypeError) {
            console.error(`Caught a type error: ${error.name} - ${error.message}`);
        } else if (error instanceof RangeError) {
            console.error(`Caught a range error: ${error.name} - ${error.message}`);
        } else {
            console.error(`Caught a generic error: ${error.name} - ${error.message}`);
        }
    } finally {
        console.log("Execution in finally block.");
    }
});

Output:

Throwing generic error:
Caught a generic error: Error - This is a generic error!
Execution in finally block.

Throwing type error:
Caught a type error: TypeError - This is a type error!
Execution in finally block.

Throwing range error:
Caught a range error: RangeError - This is a range error!
Execution in finally block.

Throwing custom error:
Caught a custom error: CustomError - This is a custom error!
Execution in finally block.

Throwing none error:
No error thrown.
Execution in finally block.

Conclusion

In JavaScript, the practice of throwing errors is a crucial technique for handling exceptional scenarios and ensuring that your code remains robust and logical. By learning to effectively use the throw statement, define custom error types, and implement try...catch blocks, you can develop more reliable JavaScript applications. To enhance the context surrounding the issues that may arise in your application, it is essential to consistently include informative error messages and consider the development of unique error types.