Error Handling in JavaScript: Try, Catch, Finally

#javascript #programming #productivity #beginners

No matter how great we are at programming sometimes our code has errors.
Errors are a natural part of programming , what matters is how effectively we handle and fix them.

In this blog we will look into these methods that gracefully handles errors.

Topics to Cover

What errors are in JavaScript
Using try and catch blocks
The finally block
Throwing custom errors
Why error handling matters

Errors

Errors are the problems or mistakes in a programming that cause it to behave incorrectly and stop running.

There are types of error which which make your code to behave incorrectly

Common types

Syntax error :- Wrong syntax
example :- Missing brackets , typo
Reference error :- Using a variable that is not defined
example :- console.log(x) when x doesn't exist
Type error :- using a value in wrong way
example :- calling something that is not a function

Above are some types of errors I commonly encounter in my daily coding.

There are ways that i handle these are gracefully lets see one by one.

Using try and catch blocks

This is primary mechanism for error handling in javascript

Here is the basic syntax for try..catch


try {
  // some code 
} catch (err) {
  // this will run only if the code in the try block errors-out
}

It works like :

First the code in try{} block is executed.
If there is no error the catch(err){} block is ignored.
If an error occurs, Then the try{} execution is stopped and the catch(err){} block will start executing.

The err variable will contain an error object with details about what happened.

Lets take some examples

Here is the example we will misspell a variable name


let hello = 2;
try {
  console.log(hilleo + 4);
} catch (e) {
  console.log('Error -', e);
}

Output of the above code :


Error - ReferenceError: hilleo is not defined

The finally block

You can also use a finally{} block to ensure that some code runs no matter if the try block executes or not.


let hello = 2;
try {
  console.log(hilleo + 4);
} catch (e) {
  console.log('Error -', e);
}finally{
  console.log("Like this blog")
}

Output of the above code :


Error - ReferenceError: hilleo is not defined
Like this blog

Throwing Custom Errors

There are some problem oftentimes that we cant able to detect where the error is coming from or its hard to understand to catch pure JavaScript errors.

For this we can make use of throw statement to throw our own errors in a try block so that can can be caught and we can deal with it gracefully.


try{
   const {email , password} = req.body 
   if(!email || !password){
     throw new Error("Fields are missing")
   } 

   console.log("Email fetch")
  }catch(err){
    console.log("error" , err)
  }