CODEWITHSUNDEEP
javascriptphpajaxcaching
user6612209
user6612209

Reputation:

Cached result in AJAX

I am trying to learn AJAX from w3schools.com . But i can't understand follwing example:

xhttp.open("GET", "demo_get.asp", true); xhttp.send();

In the example above, you may get a cached result. To avoid this, add a unique ID to the URL:

xhttp.open("GET", "demo_get.asp?t=" + Math.random(), true); xhttp.send();

Question1: What is cached result and how it is avoided by adding unique ID to the url?

Question2: When we send request(data) to the specific php file we can see data in specific file only by using $_REQUEST global variable ,why we can't use $_GET global variable (when we are sending data by GET Method)?

thanks in advance.

Upvotes: 0

Views: 871

Answers (3)

Ernest Thankson
Ernest Thankson

Reputation: 1

QUESTION 1 By cached results, I think they mean that the response retrieved by your XMLHttpRequest object is temporarily stored/cached by your browser. That means that the next time you try to get a response, you will get the old (cached response) unless you are using an id that is different from that of the cached response. In other words, unique ids ensure you are reaching whatever file you are retrieving data from whenever you ask for a response.

Upvotes: 0

25r43q
25r43q

Reputation: 623

Web cache simply means that the file stays in the browser, thus speeding up your browsing since you dont need to get the same files over and over.

1: By adding a random string or a timestamp as a parameter the browser treats it as a new file all the time.

remotefile.js?ts=123 is not the same as remotefile remotefile.js?ts=124

2: In php 5.3+ you get the data by looking at the globals for the specific request type.

$_GET holds all get parameters (ie the part of the URL after ?)
$_POST holds an array of all POST.parameters
file_get_contents('php://input') holds the json in a json-request

The reason you can't see attadhed GET-data using $_GET is because a get reuest only handles URL-parameters. If you want to sent data, look into POST.

http://www.w3schools.com/jquery/ajax_post.asp

Upvotes: 1

Abdennour TOUMI
Abdennour TOUMI

Reputation: 93163

Question 1 :

  1. Cached Result:

    • Who Cache ? Browser
    • What cache ? : For each request (URL) , browser caches response (result)
    • Where Cache ? Temporary memory of Browser (in HDD of computer)

  2. "demo_get.asp?t=" + Math.random() :

    This will change the URL for each call , so, for example , if demo_get.asp?t=32332 is cached , it will not influence demo_get.asp?t=43948348 . Thanks to Math.random()

Question 2 :

According to Method used in client side , you will be able to handle request in th server-side.

  • GET method : 

       //client side 
    xhttp.open("GET", "demo_get.asp?t=" + Math.random(), true);
  //server side 
     $_GET

  • POST method : 

       //client side 
     xhttp.open("POST", "demo_get.asp?t=" + Math.random(), true);
   //server side 
     $_POST

Upvotes: 1

Related Questions