How do I implement onchange of <input type="text"> with jQuery?

As @pimvdb said in his comment,

Note that change will only fire when the input element has lost focus. There is also the input event which fires whenever the textbox updates without it needing to lose focus. Unlike key events it also works for pasting/dragging text.

(See documentation.)

This is so useful, it is worth putting it in an answer. Currently (v1.8*?) there is no .input() convenience fn in jquery, so the way to do it is

$('input.myTextInput').on('input',function(e){
 alert('Changed!')
});

I would suggest using the keyup event something like below:

$('elementName').keyup(function() {
 alert("Key up detected");
});

There are a few ways of achieving the same result so I guess it's down to preference and depends on how you want it to work exactly.

Update: This only works for manual input not copy and paste.

For copy and paste I would recommend the following:

$('elementName').on('input',function(e){
 // Code here
});

Here's the code I use:

$("#tbSearch").on('change keyup paste', function () {
    ApplyFilter();
});

function ApplyFilter() {
    var searchString = $("#tbSearch").val();
    //  ... etc...
}

<input type="text" id="tbSearch" name="tbSearch" />

This works quite nicely, particularly when paired up with a jqGrid control. You can just type into a textbox and immediately view the results in your jqGrid.

There is one and only one reliable way to do this, and it is by pulling the value in an interval and comparing it to a cached value.

The reason why this is the only way is because there are multiple ways to change an input field using various inputs (keyboard, mouse, paste, browser history, voiceinput etc.) and you can never detect all of them using standard events in a cross-browser environment.

Luckily, thanks to the event infrastructure in jQuery, it’s quite easy to add your own inputchange event. I did so here:

$.event.special.inputchange = {
    setup: function() {
        var self = this, val;
        $.data(this, 'timer', window.setInterval(function() {
            val = self.value;
            if ( $.data( self, 'cache') != val ) {
                $.data( self, 'cache', val );
                $( self ).trigger( 'inputchange' );
            }
        }, 20));
    },
    teardown: function() {
        window.clearInterval( $.data(this, 'timer') );
    },
    add: function() {
        $.data(this, 'cache', this.value);
    }
};

Use it like: $('input').on('inputchange', function() { console.log(this.value) });

There is a demo here: http://jsfiddle.net/LGAWY/

If you’re scared of multiple intervals, you can bind/unbind this event on focus/blur.

<input id="item123" class="firstName" type="text" value="Hello there" data-someattr="CoolExample" />

$(".firstName").on('change keyup paste', function () {
   var element = $(this);
   console.log(element);
   var dataAttribute = $(element).attr("data-someattr");
   console.log("someattr: " + dataAttribute );
});

I recommend use this keyword in order to get access to the entire element so your are able do everything you need with this element.

If you want to trigger the event as you type, use the following:

$('input[name=myInput]').on('keyup', function() { ... });

If you want to trigger the event on leaving the input field, use the following:

$('input[name=myInput]').on('change', function() { ... });

The following will work even if it is dynamic/Ajax calls.

Script:

jQuery('body').on('keyup','input.addressCls',function(){
  console.log('working');
});

Html,

<input class="addressCls" type="text" name="address" value="" required/>

I hope this working code will help someone who is trying to access dynamically/Ajax calls...

$("input").change(function () {
    alert("Changed!");
});

$("input").keyup(function () {
    alert("Changed!");
});

You can do this in different ways, keyup is one of them. But i am giving example below with on change.

$('input[name="vat_id"]').on('change', function() {
    if($(this).val().length == 0) {
        alert('Input field is empty');
    }
});

NB: input[name="vat_id"] replace with your input ID or name.

You could simply work with the id

$("#your_id").on("change",function() {
    alert(this.value);
});

This worked for me. If field with name fieldA is clicked or any key entered it updates field with id fieldB.

jQuery("input[name='fieldA']").on("input", function() {
    jQuery('#fieldB').val(jQuery(this).val());
});

You could use .keypress().

For example, consider the HTML:

<form>
  <fieldset>
    <input id="target" type="text" value="Hello there" />
  </fieldset>
</form>
<div id="other">
  Trigger the handler
</div>

The event handler can be bound to the input field:

$("#target").keypress(function() {
  alert("Handler for .keypress() called.");
});

I totally agree with Andy; all depends on how you want it to work.

MVP:

<input type="text" id="query">
<script src="https://code.jquery.com/jquery-3.7.1.min.js" integrity="sha256-/JqT3SQfawRcv/BIHPThkBvs0OEvtFFmqPF/lYI/Cxo=" crossorigin="anonymous"></script>
<script type="text/javascript"> 
    
$(document).on('change keyup paste', '#query', function(e) {
    console.log(e.target.value);
});

</script>

It is worth to mention that if the form element was appended with jquery, it will not work, you need to register the event with $(document) like this:

$(document).on('change', 'input', function() {});
//or
$(document).on('change', '.inputclass', function() {});
//or
$(document).on('change', '#inputid', function() {});