Saturday, December 16, 2006

A stupid Ajax cache problem solution

One of the common problem using Ajax (Flash too) interactions is the cache.
There are a lot of valid PHP, Python, JSP and .NET solutions but browser compatibility is often a question mark.

You could implement easyly and directly a client solution and this is just another proposal.

function noCache(uri){return uri.concat(/\?/.test(uri)?"&":"?","noCache=",(new Date).getTime(),".",Math.random()*1234567)};

exactly 123 bytes to solve cache problems and this is the func description:

function noCache(
// uri string to open

return uri.concat(
// concat String prototype,
// the fastest way to produce
// a complete string using multiple values

/\?/.test(uri) ?
// if uri has a query string

// add last value using & separator char

// else
// add a query string to this url

// this should be a "cool name" for generated key

(new Date).getTime(),
// the noCache value will be milliseconds
// from 1970/01/01

// plus a dot ...

// ... and a random value using
// a "big" integer as generator

// then this is a return example using uri:

// while this is an example using uri:

You could test directly in a loop, a benchmark that many other sites didn't test ...

i = 0, // many loops
max = 10000, // max i value
uri = document.location.href, // this href
obj = {}; // a generic object
i < max; // while i is less than max
i++ // increment the i value
) {
if(!obj[noCache(uri)]) // if obj has not a nocache(uri) key
obj[noCache(uri)] = true; // set them as true
else { // else if obj has just the returned nocache(uri) key
i = max;
alert("noCache doesn't work"); // this method is not so cool

A script that use Ajax requestes inside a loop is not a good script (I suppose) but this kind of demostration can show You that generated no-cache collisions probability are quite impossible.

A usage example should be this one:"get", noCache(myUri), true);
// or ..."post", noCache(myUri2), true);

Finally these are some F.A.Q.

Why there is a key and a value and not just a random value to perfom without caching problems ?
- because some server-side code should loop over GET or POST keys and in this way it should know that noCache is a not useful parameter to parse or to check. In other cases a server-side code should consider generated radom value as a key.

Why there is a getTime plus a random value and not just the first one ?
- because some client application should call more than a single request at the same time

Why there is a full stop between getDate and random value ?
- because if client date is modified there are less possibilities that generated value was just used (paranoia style)

I think these F.A.Q. are enought and I hope You'll find this simple function useful :-)

P.S. with ActionScript just change the regExp replacing with uri.indexOf("?") >= 0

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