Exception
  • try ... catch ... finally
  • throw, throw exception
    • try ... catch ... finally
    try
{
	addalert("Welcome to Javascript ...");
}
catch(err)
{
	console.log("Catch error ...");
	console.log(err);
}
finally
{
	console.log("Finally statements ...");
}
    throw
    <input id="demo" type="text" onchange="validate()">
<script type="text/javascript">
function f()
{
	var x = document.getElementById("demo").value;
	if (x == "") throw "Empty";
	if (isNaN(x)) throw "Not a Number ...";
}

function validate()
{
	try{
		f();
	}
	catch(err)
	{
		console.log(err);
		return;
	}
		console.log("Input is legal ...");
	}
</script>
    Error Properties
  • name, error name
  • message, error message
    • onerror( ) Method
  • The onerror event handler was the first feature to facilitate error handling in JavaScript
  • The error event is fired on the window object whenever an exception occurs on the page
    • <html> 
   <head> 
      <script type = "text/javascript"> 
         function myFunc()
         {
            throw new Error("Erorr ...");
         }

         window.onerror  =  function (msg, url, line) {  
            document.write ("An error occurred.");
            console.log(msg); // Error Message
            console.log(url); // URL
            console.log(line); // Line Number
         } 
      </script> 
   </head> 

   <body> 
      <p>Click the following to see the result:</p> 
      <form> 
         <input type = "button" value = "Click Me" onclick = "myFunc();" /> 
      </form> 
   </body> 
</html>
    Custom Errors
    function MyError(message) { 
   this.name = 'MyError'; 
   this.message = message || 'Error raised with default message'; 
}

function f() {throw new MyError("Error ...");}
function f2() {throw new MyError();} // use the default error message

try
{
	f();
}
catch (e)
{
	console.log(e.name);
	console.log(e.message);
}

try
{
	f2();
}
catch (e)
{
	console.log(e.name);
	console.log(e.message);
}
    Error Types
  • EvalError, An error has occurred in the eval() function
  • RangeError, A number "out of range" has occurred
  • ReferenceError, An illegal reference has occurred
  • SyntaxError, A syntax error has occurred
  • TypeError, A type error has occurred
  • URIError, An error in encodeURI() has occurred
    • Reference
  • Tutorialspoint