How to run a function only once when it's triggered by both focus and click events

Question

I have an input element with 2 events attached: focus and click. They both fire off the same helper function.

When I tab to the input, the focus event fires and my helper is run once. No problems there.

When the element already has focus, and I click on it again, the click event fires and my helper runs once. No problems there either.

But when the element does not have focus, and I click on it, BOTH events fire, and my helper is run TWICE. How can I keep this helper only running once?

I saw a couple similar questions on here, but didn't really follow their answers. I also discovered the .live jQuery handler, which seems like it could work if I had it watch a status class. But seems like there should be a simpler way. The .one handler would work, except I need this to work more than once.

Thanks for any help!

Answer 1

Improving on @Christopher Meyers solution.

Some intro: Before the click event fires, 2 events are preceding it, mousedown & mouseup, if the mousedown is fired, we know that probably the mouseup will fire. Therefore we probably wouldn't like that the focus event handler would execute its action. One scenario in which the mouseup wouldn't fire is if the user starts clicking the button then drags the cursor away, for that we use the blur event.

  let mousedown = false;

  const onMousedown = () => {
    mousedown = true;
  };

  const onMouseup = () => {
    mousedown = false;
    // perform action
  };

  const onFocus = () => {
    if (mousedown) return;
    // perform action
  };

  const onBlur = () => {
    mousedown = false;
    // perform action if wanted
  };

The following events would be attached:

const events = [
    { type: 'focus', handler: onFocus },
    { type: 'blur', handler: onBlur },
    { type: 'mousedown', handler: onMousedown },
    { type: 'mouseup', handler: onMouseup }
];

Answer 2

The best answer here would be to come up with a design that isn't trying to trigger the same action on two different events that can both occur on the same user action, but since you haven't really explained the overall problem you're coding, we can't really help you with that approach.

One approach is to keep a single event from triggering the same thing twice is to "debounce" the function call and only call the function from a given element if it hasn't been called very recently (e.g. probably from the same user event). You can do this by recording the time of the last firing for this element and only call the function if the time has been longer than some value.

Here's one way you could do that:

function debounceMyFunction() {
    var now = new Date().getTime();
    var prevTime = $(this).data("prevActionTime");
    $(this).data("prevActionTime", now);
    // only call my function if we haven't just called it (within the last second)
    if (!prevTime || now - prevTime > 1000) {
        callMyFunction();
    }
}

$(elem).focus(debounceMyFunction).click(debounceMyFunction);

Answer 3

It seems to me that you don't actually need the click handler. It sounds like this event is attached to an element which when clicked gains focus and fires the focus handler. So clicking it is always going to fire your focus handler, so you only need the focus handler.

If this is not the case then unfortunately no, there is no easy way to achieve what you are asking. Adding/removing a class on focus and only firing the click when the class isn't present is about the only way I can think of.

I have it - 2 options

1 - bind the click handler to the element in the focus callback

2 - bind the focus and the click handler to a different class, and use the focus callback to add the click class and use blur to remove the click class

Answer 4

You could use a timeout which get's cleared and set. This would introduce a slight delay but ensures only the last event is triggered.

$(function() {
  $('#field').on('click focus', function() {
    debounce(function() {
        // Your code goes here.
        console.log('event');
    });
  });  
});

var debounceTimeout;

function debounce(callback) {
  clearTimeout(debounceTimeout);
  debounceTimeout = setTimeout(callback, 500);
}

Here's the fiddle http://jsfiddle.net/APEdu/

UPDATE

To address a comment elsewhere about use of a global, you could make the doubleBounceTimeout a collection of timeouts with a key passed in the event handler. Or you could pass the same timeout to any methods handling the same event. This way you could use the same method to handle this for any number of inputs.

Answer 5

Thanks for the great discussion everybody. Seems like the debouncing solution from @jfriend00, and the mousedown solution from Chris Meyers, are both decent ways to handle it.

I thought some more, and also came up with this solution:

// add focus event
$myInput.focus(function() {
    myHelper();
    // while focus is active, add click event
    setTimeout(function() {
        $myInput.click(function() {
            myHelper(); 
        });
    }, 500);    // slight delay seems to be required
});

// when we lose focus, unbind click event
$myInput.blur(function() {
    $myInput.off('click');
});

But seems like those others are slightly more elegant. I especially like Chris' because it doesn't involve dealing with the timing.

Thanks again!!

Answer 6

This worked for me:

http://jsfiddle.net/cjmemay/zN8Ns/1/

$('.button').on('mousedown', function(){
    $(this).data("mouseDown", true);
});

$('.button').on('mouseup', function(){
    $(this).removeData("mouseDown");
});

$('.button').on('focus', function(){
    if (!$(this).data("mouseDown"))
        $(this).trigger('click.click');
});

$(".button").on('click.click',evHandler);

Which I stole directly from this: https://stackoverflow.com/a/9440580/264498

Answer 7

Live demo (click).

I'm just simply setting a flag to gate off the click when the element is clicked the first time (focus given). Then, if the element gets focus from tabbing, the flag is also removed so that the first click will work.

var $foo = $('#foo');

var flag = 0;
$foo.click(function() {
  if (flag) {
    flag = 0;
    return false;
  }
  console.log('clicked');
});

$foo.focus(function() {
  flag = 1;
  console.log('focused');
});

$(document).keyup(function(e) {
  if (e.which === 9) {
    var $focused = $('input:focus');
    if ($focused.is($foo)) {
      flag = 0;
    }
  }
});