exit() is a function in PHP that is used to terminate script execution immediately. Common uses include: 1. Terminate the script in advance when an exception is detected, such as the file does not exist or verification fails; 2. Output intermediate results during debugging and stop execution; 3. Call exit() after redirecting in conjunction with header() to prevent subsequent code execution; In addition, exit() can accept string parameters as output content or integers as status code, and its alias is die().

To merge two PHP arrays and keep unique values, there are two main methods. 1. For index arrays or only deduplication, use array_merge and array_unique combinations: first merge array_merge($array1,$array2) and then use array_unique() to deduplicate them to finally get a new array containing all unique values; 2. For associative arrays and want to retain key-value pairs in the first array, use the operator: $result=$array1 $array2, which will ensure that the keys in the first array will not be overwritten by the second array. These two methods are applicable to different scenarios, depending on whether the key name is retained or only the focus is on

The rational use of semantic tags in HTML can improve page structure clarity, accessibility and SEO effects. 1. Used for independent content blocks, such as blog posts or comments, it must be self-contained; 2. Used for classification related content, usually including titles, and is suitable for different modules of the page; 3. Used for auxiliary information related to the main content but not core, such as sidebar recommendations or author profiles. In actual development, labels should be combined and other, avoid excessive nesting, keep the structure simple, and verify the rationality of the structure through developer tools.

The way to process raw POST data in PHP is to use $rawData=file_get_contents('php://input'), which is suitable for receiving JSON, XML, or other custom format data. 1.php://input is a read-only stream, which is only valid in POST requests; 2. Common problems include server configuration or middleware reading input streams, which makes it impossible to obtain data; 3. Application scenarios include receiving front-end fetch requests, third-party service callbacks, and building RESTfulAPIs; 4. The difference from $_POST is that $_POST automatically parses standard form data, while the original data is suitable for non-standard formats and allows manual parsing; 5. Ordinary HTM

There are two ways to create an array in PHP: use the array() function or use brackets []. 1. Using the array() function is a traditional way, with good compatibility. Define index arrays such as $fruits=array("apple","banana","orange"), and associative arrays such as $user=array("name"=>"John","age"=>25); 2. Using [] is a simpler way to support since PHP5.4, such as $color

Doctype is a statement that tells the browser which HTML standard to use to parse the page. Modern web pages only need to be written at the beginning of the HTML file. Its function is to ensure that the browser renders the page in standard mode rather than weird mode, and must be located on the first line, with no spaces or comments in front of it; there is only one correct way to write it, and it is not recommended to use old versions or other variants; other such as charset, viewport, etc. should be placed in part.

The web page structure needs to be supported by core HTML elements. 1. The overall structure of the page is composed of , , which is the root element, which stores meta information and displays the content; 2. The content organization relies on title (-), paragraph () and block tags (such as ,) to improve organizational structure and SEO; 3. Navigation is implemented through and implemented, commonly used organizations are linked and supplemented with aria-current attribute to enhance accessibility; 4. Form interaction involves , , and , to ensure the complete user input and submission functions. Proper use of these elements can improve page clarity, maintenance and search engine optimization.

When using HTML5SSE, the methods to deal with reconnection and errors include: 1. Understand the default reconnection mechanism. EventSource retrys 3 seconds after the connection is interrupted by default. You can customize the interval through the retry field; 2. Listen to the error event to deal with connection failure or parsing errors, distinguish error types and execute corresponding logic, such as network problems relying on automatic reconnection, server errors manually delay reconnection, and authentication failure refresh token; 3. Actively control the reconnection logic, such as manually closing and rebuilding the connection, setting the maximum number of retry times, combining navigator.onLine to judge network status to optimize the retry strategy. These measures can improve application stability and user experience.