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| JavaScript Error Handling Techniques Every Developer Should Know |
Mistakes in coding have to be handled in a structured manner. If errors can be caught and thrown according to program specifications, execution will be predictable even when unexpected things happen. Mistakes are expected or demonstrated during program runtime , event handling can forestall program crashes, so debugging becomes simple. This post refers to the different error handling techniques in JavaScript.
Get on to the errors only if you understand the variety possible in JavaScript it errors. The common types of these are:
- Syntax errors: They are errors caused by improper writing of the code to the right syntax of the language. This means that this code cannot execute.
- Runtime Errors: They are errors that occur during the execution of the program; they are majorly caused by invalid operations such as trying to access some variable that has not been defined.
- Logical Errors: These do not cause the program to fail. They result in wrong behavior or output.
- Custom errors: These are user-defined errors, typically created to receive specific conditions during code execution.
2. Using try...catch for Error Handling
- The typical method for handling errors in JavaScript is through the try...catch statement Incidentally, any code can be executed and any errors are captured if need be. The basic form is:
try {
// Code that may throw an error
} catch (error) {
// Code that runs if an error is caught
}
In this layout:
- A try involves an error causing an error.
- Block-determining code executes when an error occurs.
try {
let result = someFunction();
} catch (error) {
console.log('An error occurred: ' + error.message);
}
In the above example, in the case that someFunction() throws an error, the catch block will intercept it, and in this case, an error message will be logged.
Now, whenever an exception is caught in the catch block, it gets the error passed as an argument to the catch clause. This argument is the error object that can be used in showing information about the error of the application. The following are some of the properties of the error object.
- message: A description of the error.
- name: The type of error.
- stack: The stack trace, which shows where the error occurred in the code.
Example:
try {
let x = y; // ReferenceError because 'y' is not defined
} catch (error) {
console.log(error.name); // "ReferenceError"
console.log(error.message); // "y is not defined"
console.log(error.stack); // Stack trace
}
JavaScript allows throwing the error as per the requirement using throw statement from your perspective. Whenever you define "throw," then an error is created and used, which, in addition to ending the execution of the program, treats error information. You may throw an error object or throw any other value.
Example:
function validateAge(age){
if(age<18){
throw new Error("Age must be greater than 18");
}
return true;
}
try{
validateAge(16);
}
catch(error){
console.log(error.message); // "Age must be greater than 18"
}
An example in which throwing an error is considered valid if the age is less than 18 and the error is caught and logged by using only a try block.
JavaScript is able to handle many categories of exceptions that are thrown in the same block with a try...catch statement. This is done by filtering what error actually occurred and reacting accordingly.
Exercise:
try {
let result = someFunction();
} catch (error) {
if (error instanceof TypeError) {
console.log('Type error occurred');
} else if (error instanceof ReferenceError) {
console.log('Reference error occurred');
} else {
console.log('Unknown error occurred');
}
}
This provides flexibility in the handling of different error types.
The main feature of a finally block is that it follows the catch block and is optional. This is executed even if an error is thrown after the try block, and then the catch block.This is important because all the clean-up operations can be written in this optional block, like closing database connections or releasing resources that are being used within the execution of the attempted code.
Example:
try {
let result = someFunction();
} catch (error) {
console.log('Error: ' + error.message);
} finally {
console.log('This will always run');
}
In this example, the finally block will always run no matter what, even if an error is thrown.
7. Handling Asynchronous Errors
Error handling is quite a different story when it comes to an asynchronous code. There is no mechanism in place to cater to the exceptions in asynchronous operations by JS automatically.
a. Using .catch() with Promises
The .catch() method is to be used to catch errors in promises. It catches any possible rejection occurring during the promise execution.
Example:
let promise = new Promise((resolve, reject) => {
let success = false;
if (success) {
resolve('Success');
} else {
reject('Failure');
}
});
promise.then(result => {
console.log(result);
}).catch(error => {
console.log(error); // "Failure"
});
b. Using try...catch with async/await
In asynchronous functions with the help of async/await, they are easier to handle the errors with the help of try...catch blocks.
Example:
async function fetchData() {
try {
let response = await fetch('https://api.example.com/data');
let data = await response.json();
console.log(data);
} catch (error) {
console.log('Error fetching data: ' + error.message);
}
}
To handle and debug errors effectively, follow the steps below:
- Use console.log: method of logging: This method is useful in logging messages errors and other information to the console for traceability to issues.
- Using the debugger statement: This helps code debugging by pausing the code execution until the examination of variables at distinct points.
- Test and review the code: Before wrapping up coding quite closely, make sure to run it through several different environments and use cases to detect potential errors early on.
Conclusion
By using the try...catch statement, throwing custom errors with throw, and handling asynchronous errors effectively, we would ensure that code runs smoothly even if something unexpected comes up. Proper error handling is good for code to be maintained and reliable because it makes it easier to debug and troubleshoot when a problem arises.
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