Regular expression

• In PHP, regular expressions are strings composed of delimiters, a pattern and optional modifiers.
• Following function allow us to use regular expression
  • preg_match(): Returns 1 if the pattern was found in the string and 0 if not
  • preg_match_all(): Returns the number of times the pattern was found in the string, which may also be 0
  • preg_replace(): Returns a new string where matched patterns have been replaced with another string

preg_match()

$str = "Visit W3Schools";
$pattern = "/w3schools/i";
echo preg_match($pattern, $str);

// output --> 1

preg_match_all()

$str = "The rain in SPAIN falls mainly on the plains.";
$pattern = "/ain/i";
echo preg_match_all($pattern, $str);

// output --> 4 

preg_replace()

$str = "Visit Microsoft!";
$pattern = "/microsoft/i";
echo preg_replace($pattern, "W3Schools", $str);

// output --> Visit W3Schools!

GET & POST

• $_GET is an array of variables passed to the current script via the URL parameters.
• $_POST is an array of variables passed to the current script via the HTTP POST method.

Form Validation

<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">

• $_SERVER["PHP_SELF"] is a superglobal variable that returns tha path of filename
• $_SERVER["PHP_SELF"] sends the submitted form data to the page itself instead of jumping to a different page.
• $_SERVER["PHP_SELF"] variable can be used by hackers

<form method="post" action="test_form.php/"><script>alert('hacked')</script>

• The above code add script tag with alter command. To avoid this we use htmlspecialchars

<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">

• htmlspecialchars() function converts special characters to HTML entities

<form method="post" action="test_form.php/&quot;&gt;&lt;script&gt;alert('hacked')&lt;/script&gt;">

• For form field validation we do following things
  • trim data using trim function
  • remove backslash using stripslashes function
  • and use htmlspecialchars to convert html code to html entities

PHP Date

• In php date() function is used to get the date and time in specified
• Following are some characters for date
  • d: represents the day of month (01-31)
  • m: represents the month (01-12)
  • Y: represents year in four digits
  • l: represents day of week
• Following are some characters for time
  • H: 24 hours format (00-23)
  • h: 12 hours format (01-12)
  • i: minutes (00-59)
  • s: seconds (00-59)
  • a: lowercase am/pm
• strtotime() function is used to convert a human readable date string into a Unix timestamp (number of seconds since January 1 1970 00:00:00 GMT)

include and require Statements:

• Both are ways to include content of file in current php file
• But it has following difference
  • require will produce a fatal error and stop the script
  • include will only produce a warning and the script will continue

Midday Questions

• Main Thread in Browsers:
  • Handles user events.
  • Renders and paints HTML/CSS on the screen.
  • Runs synchronous code in scripts.
• Benefits of async-await:
  • Improved syntax over then() chaining.
  • Cleaner code, avoiding callback hell.
  • Easy error handling with try-catch.
  • Avoids callback hell problem.
• API Calls in JavaScript:
  • Methods: fetch, XMLHttpRequest, axios (3rd party), AJAX.
  • Preferred: fetch for its simplicity and compatibility with promises.
• DOM (Document Object Model):
  • Represents HTML elements in a tree structure.
  • Enables dynamic manipulation of elements, content, and styles.
  • Vital for creating dynamic web pages, updating content without refresh.
• PHP vs. JavaScript Security:
  • PHP and JavaScript serve different roles.
  • PHP runs on the server, keeping its code secure.
  • JavaScript runs in browsers, making its code visible.
  • Security depends on how and where each language is used.
• PHP Cookies vs. JavaScript Cookies:
  • PHP Cookies:
    • Server-side management.
    • Sent from the server to the client.
    • Stores less sensitive data.
    • Accessed using $_COOKIE superglobal.
  • JavaScript Cookies:
    • Client-side management.
    • Uses document.cookie to set cookies on the browser.