php - New image is created but the old one is shown JS(AJAX) -

i have ajax function

function getoutput()  {    var ajax = getrequest();   document.getelementbyid('output').innerhtml = "<br/>";   ajax.onreadystatechange = function()   {       if(ajax.readystate == 4)       {           document.getelementbyid('output').innerhtml = ajax.responsetext;       }    }   document.getelementbyid('output').innerhtml = "<br/><img src=img/ajax-loader.gif><br/><br/>";   ajax.open("get", "graph_2.php", true);   ajax.send(null); }     

html

<form >   <input type="image" src=img/button.jpg class=mygtukas    onclick='getoutput(); return false;'> </form> <span id=output></span> 

which calls php code create graph. first time works fine, when user changes graph parameters , press button again (page doesn't reload) shows old graph dough there new graph created , saved in server.

this because of cache of browser. browsers saves copy of image on computer on in temp directory. because image has same name , location previous version, loads image disk, loads allot faster (no need download again)

the solution simple. change imagename variable. used trick add random value:

instead of image.jpg, return image.jpg?_randomstringhere

the randomstring can based on few things. in php use uniqid() because unique (unless can refresh faster 1 milisec). method (as suggested in comments below), timestamp. in php time() suffice.

if want javascript solution, can allong lines of image.src = image.src +'?'+ math.random()

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it occurred me might ajaxcall itself. can use javascript suggestion stated above in ajaxcall make every call unique

math.random() documentation