Input event not working if value is changed with j

问题:

If I change the value of an input field programmatically, the input and change events are not firing. For example, I have this scenario:

var $input = $('#myinput');

$input.on('input', function() {
  // Do this when value changes
  alert($input.val());
});

$('#change').click(function() {
  // Change the value
  $input.val($input.val() + 'x');
});

<input id="myinput" type="text" />
<button id="change">Change value</button>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

The problem: The event is triggered when I type in the textfield, but not when I press the button. Is there a way to achieve this with some kind of event or otherwise without having to do it manually?

What I don't want to do: I could go through all my code to add a trigger or function call everywhere manually, but that's not what I'm looking for.

Why: The main reason I would like to do this automatically is that I have a lot of input fields and a lot of different places where I change these inputs programmatically. It would save me a lot of time if there was a way to fire the event automatically when any input is changed anywhere in my code.

回答1:

Simple solution:

Trigger input after you call val():

$input.trigger("input");

var $input = $("#myinput");

$input.on('input', function() {
  alert($(this).val());
});

$('#change').click(function() {
  // Change the value and trigger input
  $input.val($input.val() + 'x').trigger("input");
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<input id="myinput" type="text" />
<button id="change">Change value</button>

Specific solution:

As mentioned you don't want to trigger input manually. This solution triggers the event automatically by overriding val().

Just add this to your code:

(function ($) {
    var originalVal = $.fn.val;
    $.fn.val = function (value) {
        var res = originalVal.apply(this, arguments);

        if (this.is('input:text') && arguments.length >= 1) {
            // this is input type=text setter
            this.trigger("input");
        }

        return res;
    };
})(jQuery);

See JSFiddle Demo

PS

Notice this.is('input:text') in the condition. If you want to trigger the event for more types, add them to the condition.

回答2:

There are some ways on how to achieve it. Here, you can use the levelup HTML's oninput() event that occurs immediately when an element is changed and call the function.

<input id="myinput" type="text" oninput="sample_func()" />
<button id="change">Change value</button>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

.

var input = $("#myinput");

function sample_func(){
  alert(input.val());
}

$('#change').click(function() {
  input.val(input.val() + 'x');
});

---

Or this jQuery, input thing (just related to above example).

<input id="myinput" type="text" />
<button id="change">Change value</button>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

.

var input = $("#myinput");

input.on("input", function() {
  alert(input.val());
});

$('#change').click(function() {
  input.val(input.val() + 'x');
});

---

You can also use javascript setInterval() which constantly runs with a given interval time. It's only optional and best if you're doing time-related program.

<input id="myinput" type="text" />
<button id="change">Change value</button>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

.

var input = $("#myinput");

setInterval(function() { ObserveInputValue(input.val()); }, 100);

$('#change').click(function() {
  input.val(input.val() + 'x');
});

回答3:

Looks like there's no way, other than using .trigger().

Let's try the same thing using .change() event:

var $input = $("#myinput");

$input.on('change paste keyup', function() {
  alert($(this).val());
});

$('#change').click(function() {
  $input.val($input.val() + 'x').trigger("change");
});

<input id="myinput" type="text" />
<button id="change">Change value</button>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

Or you need to trigger it manually:

$('#change').click(function() {
  $input.val($input.val() + 'x').trigger("input");
});

Snippet

var $input = $("#myinput");

$input.on('input', function() {
  alert($(this).val());
});

$('#change').click(function() {
  $input.val($input.val() + 'x').trigger("input");
});

<input id="myinput" type="text" />
<button id="change">Change value</button>

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

回答4:

jQuery listeners only work on actual browser events and those aren't thrown when you change something programmatically.

You could create your own miniature jQuery extension to proxy this so that you always trigger the event but only have to do in one modular place, like so:

$.fn.changeTextField = function (value) {
  return $(this).val(value).trigger("change");
}

Then, just call your new function whenever you want to update your text field, instead of using jQuery's 'val' function:

$("#myInput").changeTextField("foo");

Here's a version working with a proxy function:

    <!DOCTYPE html>
    <html>
        <head>
            <title>Test stuff</title>
            <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.2.2/jquery.min.js"></script>
        </head>
        <body>

  <input id="myInput" type="text" />
        <button id="myButton">Change value</button>

        <script type="text/javascript">
            $.fn.changeTextField = function (value) {
             return $(this).val(value).trigger("change");
            }

            $( document ).ready(function() {
                var $input = $("#myInput");

                $input.on("change", function() {
                    alert($input.val());
                });

                $('#myButton').click(function() {
                    $("#myInput").changeTextField("foo");
                });
            });
        </script>
        </body>
    </html>

For reference, this question has really already been answered here: Why does the jquery change event not trigger when I set the value of a select using val()?

and here: JQuery detecting Programatic change event

回答5:

$input.val($input.val() + 'x')
$input.trigger('change');

The change event only fire when input blur.