Trying to add delay to jQuery AJAX request

问题

I am trying to delay an AJAX request so that it is sent out 2-3 seconds after the LAST keyup of an input cell.
So far I have managed to delay the requests, but after 2-3 seconds I get one request sent for every keyup in the field...
How can I make jQuery cancel the first ones and just send the last keyup?
Here's the code so far:

$('#lastname').focus(function(){
          $('.terms :input').val(""); //clears other search fields
}).keyup(function(){
    caps(this); //another function that capitalizes the field
    $type = $(this).attr("id"); // just passing the type of desired search to the php file
        setTimeout(function(){ // setting the delay for each keypress
                ajaxSearchRequest($type); //runs the ajax request

        }, 1000);
});

This code above, waits 1 sec then sends 4-5 AJAX requests depending on keypresses. I just want one sent after the last keyup
I have found some similar solutions in StackOverflow that use Javascript, but I have not been able to implement them to my project due to my small knowledge of programming.

[SOLVED] Final working code, thanks to @Dr.Molle:

$('#lastname').focus(function(){
          $('.terms :input').val("");
}).keyup(function(){
    caps(this);
    $type = $(this).attr("id");

    window.timer=setTimeout(function(){ // setting the delay for each keypress
            ajaxSearchRequest($type); //runs the ajax request

        }, 3000);

}).keydown(function(){clearTimeout(window.timer);});

Here's the ajaxSearchRequest code:

function ajaxSearchRequest($type){
                var ajaxRequest2;  // The variable that makes Ajax possible!

                try{
                  // Opera 8.0+, Firefox, Safari
                  ajaxRequest2 = new XMLHttpRequest();
                }catch (e){
                  // Internet Explorer Browsers
                  try{
                     ajaxRequest2 = new ActiveXObject("Msxml2.XMLHTTP");
                  }catch (e) {
                     try{
                    ajaxRequest2 = new ActiveXObject("Microsoft.XMLHTTP");
                     }catch (e){
                    // Something went wrong
                    alert("Browser error!");
                    return false;
                     }
                  }
                }

                ajaxRequest2.onreadystatechange = function(){
                  if(ajaxRequest2.readyState == 4){

                        $result = ajaxRequest2.responseText;
                        $('#resultcontainer').html($result);

                    }}


                var searchterm = document.getElementById($type).value;


                var queryString ="?searchterm=" + searchterm +"&type=" +$type;


                if(searchterm !== ""){

                ajaxRequest2.open("GET", "searchrequest.php" + 
                                 queryString, true);
                ajaxRequest2.send(null);
                }
        }

回答1:

store the timeout in a variable, so you will be able to clear recent timeouts:

clearTimeout(window.timer);
window.timer=setTimeout(function(){ // setting the delay for each keypress
                ajaxSearchRequest($type); //runs the ajax request

        }, 3000);

回答2:

What you are trying to do is called debouncing.

Here's a jquery plugin by Ben Alman that does the job.

And underscore.js includes this functionality as well.

There's really no need to hack the ajax request system. Just make sure it's called at the right moment.

回答3:

I like the Molle's answer But I would to further improve the performance

var ajaxRequest2;  // The variable that makes Ajax possible!
function getAjaxObject()
{
                try{
                  // Opera 8.0+, Firefox, Safari
                  ajaxRequest2 = new XMLHttpRequest();
                }catch (e){
                  // Internet Explorer Browsers
                  try{
                     ajaxRequest2 = new ActiveXObject("Msxml2.XMLHTTP");
                  }catch (e) {
                     try{
                    ajaxRequest2 = new ActiveXObject("Microsoft.XMLHTTP");
                     }catch (e){
                    // Something went wrong
                    alert("Browser error!");
                   // return false;
                     }
                  }
                }
  return ajaxRequest2;


 }
   getAjaxObject();

    function ajaxSearchRequest($type){



               if(typeof ajaxRequest2 =="undefined" || ajaxRequest2 == false)
                {
                  return;
                }
               ajaxRequest2.abort();

                ajaxRequest2.onreadystatechange = function(){
                  if(ajaxRequest2.readyState == 4){

                        $result = ajaxRequest2.responseText;
                        $('#resultcontainer').html($result);

                    }}


                var searchterm = document.getElementById($type).value;


                var queryString ="?searchterm=" + searchterm +"&type=" +$type;


                if(searchterm !== ""){

                ajaxRequest2.open("GET", "searchrequest.php" + 
                                 queryString, true);
                ajaxRequest2.send(null);
                }
        }

This change will abort an on going ajax request and send a fresh request. It is helpful when you

Typed-> waited 4 sec ->request sent ->typed again (response not received) ->waited 4 second->another request fires

来源：https://stackoverflow.com/questions/11308404/trying-to-add-delay-to-jquery-ajax-request