bind event only once

Question

I have the following code:

function someMethod()
{
  $(obj).click(function {});
}

someMethod is called twice and thus click event is binded twice. How can I make it bind only once?

Answer 1

If you can apply it, probably want to take a look at event.preventDefault and event.stopPropagation OR unbind and bind each time, within your method like

function someMethod()
{
  $(obj).off('click').on('click', function(e) {
    // put your logic in here 
  });
}

Answer 2

In addition to pna's answer you may wish to think about namespacing your event so you do not go around unbinding all the click events accidentally.

function someMethod() {
    $(obj).unbind('click.namespace').bind('click.namespace', function() { });
}

https://api.jquery.com/event.namespace/

Answer 3

There is no built in method to determine if you have already bound this particular function. You can bind multiple click functions to an object. For example:

$('#id').bind('click', function(){
alert('hello');
});


$('#id').bind('click', function(){
alert('goodbuy');
});

if you do the above when the object is clicked it will alert hello then goodbye. To make sure only one function is bound to the click event unbind the click event handler then bind the desired function like this:

$(obj).unbind('click').bind('click', function(){... });

Answer 4

The obvious solution is to not call someMethod() twice. If you can't fix that, then you can keep a state variable so it only ever binds once like this:

function someMethod()
{
    if (!someMethod.bound) {
        $(obj).click(function() {});
        someMethod.bound = true;
    }
}

Note: this uses a property of the function itself rather than introducing a global variable to keep track of whether it's been bound. You could also use a property on the object itself.

You can see it work here: http://jsfiddle.net/jfriend00/VHkxu/.

Answer 5

Or use jQuery's one() function which is similar to on() but only fires the event once, even if you bind it multiple times.

http://api.jquery.com/one/

Answer 6

jQuery makes calling some function possible only once pretty easy:

function someMethod()
{

     $(obj).click(function() {});
      this.someMethod = $.noop;
}

Answer 7

You can add css class to the binded elements and then filter them out:

function someMethod()
{
    $(obj).not('.click-binded')
          .click(function {})
          .addClass('click-binded');
}

This method may be used also for plugins:

  $(obj).not('.datetimepicker-applied')
        .datetimepicker()
        .addClass('datetimepicker-applied');

Answer 8

You can use this jQuery extension function.

$.fn.once = function (type, fn, uid) {
  if(uid == undefined) {
    console.error("Called $.once without uid\n", this, "\n", fn);
  }

  var dataStr = type+"-handler-"+uid;
  if(!this.data(dataStr)) {
    this.data(dataStr, true);
    this.on(type, fn);
  }
};

Instead of doing this

$("button").on("click", function(){
  alert("You Clicked On A Button");
});

Ya do this

$("button").once("click", function(){
  alert("You Clicked On A Button");
}, "btnHandler");

Now when I have a function around it

function addBtnHandler() {
  $("button").once("click", function() {
    alert("You Clicked On A Button");
  }, "btnHandler");
}

And I call it multiple times

addBtnHandler();
addBtnHandler();
addBtnHandler();

It only does it once.

Notice that the extension works by checking both uid and type. This means that you can bind different types of handlers with the same uid, you may or may not want this. To change it edit.

var dataStr = type+"-handler-"+uid;

With something like

var dataStr = "handler-"+uid;

Answer 9

This is a suggestion since I do not know your logic. May or may not work for you.

Try combining jquery live() and one() functions will give you a better result than event rebinds.

The special cases work when you have 2 DOM elements (parent & child). Live() at parent node makes sure event will be invoked, and then calls one() to dynamically register event which would be executed only once. (this provides similar functionality like rebinds).

Answer 10

If you want to bind to the object only once, you should implement a flag and stick to that object.

For example:

if($('#id') && $('#id').data('done') == null)) {
    $('#id').bind('click', function() {
        alert('hello');
    });

    $('#id').data('done', true);
}

Answer 11

I was also trying to use off and on method of jquery for binding event only once with the dom element which does not exists yet or the dom element is not yet created.

$('.select').off('event').on('event', 'selector', function(e){ // });

This code was not working properly

I came across a very lucrative method that is 'one' method. It is very useful when you want to bind an event only once.

You can find the document here http://api.jquery.com/one/

This is same as method 'on' but different with its behavior with not to stick with the event for multiple selectors.

$('body').one('click', 'selector', function(){ // do your stuff here });

Answer 12

You can achieve this with pure JS, using addEventListener method and his once option

target.addEventListener('click', handler, {once: true});

Answer 13

var bound = false;

function someMethod()
{
    if(!bound)
    {
       $(obj).click(function {});
       bound = true;
    }
}

but I would probably look into why it;s being called twice before making some kind of workaround.