javascript - Preventing double submission of data in forms -

suppose have textarea in form named urlslist user input list of urls , 1 on each line.i handle submit via ajax query follows.

$(function () {     $("#urlslist").submit(function(e) {          //prevent default functionality         e.preventdefault();          //get action-url of form         var actionurl = e.currenttarget.action;          //do own request handle results         $.ajax({             url: actionurl,             type: 'post',             datatype: 'json',             data: $("#urlslist").serialize(),             success: function(data) {                 //put result in textarea here             }         });      });  }); 

then display result of processing (i.e url each input) in textarea. works want improve old urls don't submitted server via ajax while not clearing either of textareas.

edit 1

i think need demonstrate example.

suppose urlslist textarea contain 1 url.i click on submit , result.now add url in urlslist , click on submit again.now there 2 urls in post request.how can make sure new urls sent.

using do once lib mozilla :

function executeonce() {   var argc = arguments.length,     bimplglob = typeof arguments[argc - 1] === "string";   if (bimplglob) {     argc++;   }   if (argc < 3) {     throw new typeerror("executeonce - not enough arguments");   }   var fexec = arguments[0],     skey = arguments[argc - 2];   if (typeof fexec !== "function") {     throw new typeerror("executeonce - first argument must function");   }   if (!skey || /^(?:expires|max\-age|path|domain|secure)$/i.test(skey)) {     throw new typeerror("executeonce - invalid identifier");   }   if (decodeuricomponent(document.cookie.replace(new regexp("(?:(?:^|.*;)\\s*" + encodeuricomponent(skey).replace(/[\-\.\+\*]/g, "\\$&") + "\\s*\\=\\s*([^;]*).*$)|^.*$"), "$1")) === "1") {     return false;   }   fexec.apply(argc > 3 ? arguments[1] : null, argc > 4 ? array.prototype.slice.call(arguments, 2, argc - 2) : []);   document.cookie = encodeuricomponent(skey) + "=1; expires=fri, 31 dec 9999 23:59:59 gmt" + (bimplglob || !arguments[argc - 1] ? "; path=/" : "");   return true; } 

you can make following :

     // custom helper string.prototype.s2b64 = function() { // make base64 string   return window.btoa(unescape(encodeuricomponent(this))); } string.prototype.replacearray = function(find, replace) { // replace array   var replacestring = this;   (var = 0; < find.length; i++) {     replacestring = replacestring.replace(find[i], replace[i]);   }   return replacestring; };      // here start :   var output = [];   $.each($("#urlslist textarea").first().val().split(/\n/), function(index, value) {     alert(index + ": " + value);     if (value != '')       executeonce(function(v) {         output.push(value);       }, null, value, 'urldone_' + value.s2b64().replacearray(         ["expires", "path", "domain", "secure"],          ["e_xpires", "p_ath", "d_omain", "s_ecure"]) + '');   });    alert(output); 

some part may bit odd, it's bullet-proofing manual setcookie (like use of b64 , search & replace in case unlucky , randomly cookie keyword b64 output)

and if want remove saved value, here code :

  var cookienames = document.cookie.split(/=[^;]*(?:;\s*|$)/);    // remove match pattern   (var = 0; < cookienames.length; i++) {     if (/^urldone_/.test(cookienames[i])) {       document.cookie = cookienames[i] + '=; expires=thu, 01 jan 1970 00:00:00 gmt; path=/';     }   } 

jsfiddle

this cookie based answer (by browser, refresh & restart proof).