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JavaScript: throw statement

Description

The throw statement creates a user define exception.
You can create your own exception for unexpected events and control the script properly to throw the exception in a try block and handle it in the catch block.

Syntax

throw exception;

Parameters

exception: String, integer, Boolean or an object.

Example of try..catch..throw statement

The following example checks the length of a variable called empcode. If the value of empcode is greater than 8 or less than 3 then the code throws an error and caught by the catch argument and an appropriate message will be displayed.

HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset=utf-8>
<title>JavaScript try..catch..throw Example</title>
</head>
<body>
<h1 style="color: red">JavaScript : try..catch..throw Example</h1>
<hr />
<script src="try-catch-throw-example.js"></script>
</body>
</html>

JS Code

var empcode = prompt("Input the Employee code : (Between 3 to 8 characters):","");
try
{
if(empcode.length>8)
 {
 throw "error1";
 }
else if(empcode.length<3)
 {
  throw "error2";
 }
 }
catch(err)
 {
 if(err=="error1")
 {
 console.log("The Employee code length exceed 8 characters.");
 }
 if(err=="error2")
 {
 console.log("The Employee code length is less than 3 characters");
 }
 } 
 
 

View the example in the browser

Practice the example online

See the Pen throw-1 by w3resource (@w3resource) on CodePen.


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JavaScript: Tips of the Day

How do I redirect to another webpage?

window.location.replace(...) is better than using window.location.href, because replace() does not keep the originating page in the session history, meaning the user won't get stuck in a never-ending back-button fiasco.

If you want to simulate someone clicking on a link, use location.href

If you want to simulate an HTTP redirect, use location.replace.

// similar behavior as an HTTP redirect
window.location.replace("http://stackoverflow.com");

// similar behavior as clicking on a link
window.location.href = "http://stackoverflow.com";

Ref: https://bit.ly/37JdWH8