In Laravel, {{ $username }} and {!! $username !!} displays dynamic content within a Blade template. However, they have different behaviors depending on the context in which they are used.

{{ $username }} is used to display escaped output. This means that any special characters in the variable's value, such as HTML tags or JavaScript code, will be converted to their corresponding HTML entities to prevent them from being interpreted as code. This is done to help prevent cross-site scripting (XSS) attacks, where malicious code is injected into a web page.

{!! $username !!} is used to display unescaped output. This means the variable's value will be displayed exactly as it is, without any special characters being converted to HTML entities. This is useful when displaying HTML markup or other special characters.

However, using unescaped output can be risky, especially if the variable's value comes from user input. It can make your application vulnerable to XSS attacks. Therefore, you should always sanitize user input before displaying it on a web page and use the escaped output ({{ $variable }}) by default unless you have a good reason to use the unescaped output ({!! $variable !!}).

BY Best Interview Question ON 01 Mar 2023