Exception Handling

It is a process or method which is used for handling the abnormal statements in the code and executing them. It also enables to handle the flow control of the code/program.

For handling the code, various handlers are used that process the exception and execute the code. For example, the Division of a non-zero value with zero will result into infinity always, and it is an exception. Thus, with the help of exception handling, it can be executed and handled.

A throw statement is used to raise an exception. It means when an abnormal condition occurs, an exception is thrown using throw.

The thrown exception is handled by wrapping the code into the try…catch block. If an error is present, the catch block will execute, else only the try block statements will get executed.


Types of errors

While coding, there can be three types of errors in the code:-

  • Syntax Error:- When a user makes a mistake in the pre-defined syntax of a programming language, a syntax error may appear.
  • Runtime Error:- When an error occurs during the execution of the program, such an error is known as Runtime error. The codes which create runtime errors are known as Exceptions. Thus, exception handlers are used for handling runtime errors.
  • Logical Error: An error which occurs when there is any logical mistake in the program that may not produce the desired output, and may terminate abnormally. Such an error is known as Logical error.

Javascript try…catch

This is a commonly used statement in various programming languages. Basically, it is used to handle the error-prone part of the code.

It initially tests the code for all possible errors it may contain, then it implements actions to tackle those errors (if occur). A good programming approach is to keep the complex code within the try…catch statements.

Let’s discuss each block of statement individually:

try{} statement:- Here, the code which needs possible error testing is kept within the try block. In case any error occur, it passes to the catch{} block for taking suitable actions and handle the error. Otherwise, it executes the code written within.

catch{} statement:- This block handles the error of the code by executing the set of statements written within the block. This block contains either the user-defined exception handler or the built-in handler. This block executes only when any error-prone code needs to be handled in the try block. Otherwise, the catch block is skipped.

Syntax:-
try{  
	expression; 
} //code to be written.  
	
catch(error){  
	expression; 
} // code for handling the error.  

Throw statements are used for throwing user-defined errors. User can define and throw their own custom errors. When throw statement is executed, the statements present after it will not execute. The control will directly pass to the catch block.

Input:-
 <script>  
	   try{  
          var a=2;  
          if(a==2)  
          document.write("ok");  
     }  
     catch(Error){  
         document.write("Error found"+e.message);  
     }  
     finally{  
        document.write("Value of a is 2 ");  
     }
</script>

Output:-