This tutorial aims to guide you through the process of preventing verbose error messages in HTML development. Verbose error messages might reveal sensitive information that could be used to exploit vulnerabilities in your system. By the end of this tutorial, you will be able to hide these messages and make your website more secure.
You will learn:
Prerequisites:
Basic understanding of HTML and JavaScript is required.
Verbose error messages provide detailed insight into what went wrong when an error occurred. This can include sensitive information like server paths, database details, or other system-related information. To prevent verbose error messages, we can handle errors properly in our code.
Error Handling:
Error handling involves capturing and dealing with errors in a manageable and predictable manner. Instead of letting the program crash, we can use error handling techniques to log errors, show a user-friendly message to the user, or even recover from the error.
Example 1: HTML form with JavaScript error handling
<html>
<head>
<title>Form</title>
<script>
function validateForm() {
var x = document.forms["myForm"]["fname"].value;
if (x == "") {
alert("Name must be filled out");
return false;
}
}
</script>
</head>
<body>
<form name="myForm" action="/submit" onsubmit="return validateForm()" method="post">
Name: <input type="text" name="fname">
<input type="submit" value="Submit">
</form>
</body>
</html>
In this example, if the form is submitted without filling the name field, an alert box is shown with the message "Name must be filled out". The form is not submitted until the name field is filled out.
Example 2: Handling errors in JavaScript
try {
// Code that may throw an error
var x = 0;
var y = 10 / x;
} catch (error) {
console.log('An error occurred, but it was handled gracefully');
}
In this example, dividing by zero will cause an error. Instead of letting the program crash, we catch the error and log a message.
In this tutorial, we learned about verbose error messages and why they should be prevented. We also learned how to handle errors in our code to prevent such messages.
Next Steps:
Learn more about error handling in JavaScript and other programming languages.
Additional Resources:
Exercise 1:
Create an HTML form that validates the input for a password field. If the password is less than 8 characters, show an alert message and prevent the form from being submitted.
Solution:
<html>
<head>
<title>Form</title>
<script>
function validateForm() {
var x = document.forms["myForm"]["pwd"].value;
if (x.length < 8) {
alert("Password must be at least 8 characters long");
return false;
}
}
</script>
</head>
<body>
<form name="myForm" action="/submit" onsubmit="return validateForm()" method="post">
Password: <input type="password" name="pwd">
<input type="submit" value="Submit">
</form>
</body>
</html>
Exercise 2:
Write a JavaScript function that throws an error if the argument passed is not a number. Catch this error in your code and log a custom error message.
Solution:
function checkNumber(n) {
if (typeof n !== 'number') {
throw new Error('Argument is not a number');
}
}
try {
checkNumber('hello');
} catch (error) {
console.log('A custom error occurred: ' + error.message);
}
In this solution, the checkNumber function checks if the argument is a number. If it's not, it throws an error. We then use a try-catch block to catch this error and log a custom message.