[javascript] html <input type="text" /> onchange event not working

I am trying to do some experiment. What I want to happen is that everytime the user types in something in the textbox, it will be displayed in a dialog box. I used the onchange event property to make it happen but it doesn't work. I still need to press the submit button to make it work. I read about AJAX and I am thinking to learn about this. Do I still need AJAX to make it work or is simple JavaScript enough? Please help.

index.php

<script type="text/javascript" src="javascript.js"> </script>

<form action="index.php" method="get">
 Integer 1: <input type="text" id="num1" name="num1" onchange="checkInput('num1');" /> <br />
 Integer 2: <input type="text" id="num2" name="num2" onchange="checkInput('num2');" /> <br />
 <input type="submit" value="Compute" />
</form>

javascript.js

function checkInput(textbox) {
 var textInput = document.getElementById(textbox).value;

 alert(textInput); 
}

Firstly, what 'doesn't work'? Do you not see the alert?

Also, Your code could be simplified to this

<input type="text" id="num1" name="num1" onkeydown="checkInput(this);" /> <br />

function checkInput(obj) {
    alert(obj.value); 
}

Use .on('input'... to monitor every change to an input (paste, keyup, etc) from jQuery 1.7 and above.

For static and dynamic inputs:

$(document).on('input', '.my-class', function(){
    alert('Input changed');
});

For static inputs only:

$('.my-class').on('input', function(){
    alert('Input changed');
});

JSFiddle with static/dynamic example: https://jsfiddle.net/op0zqrgy/7/

onkeyup worked for me. onkeypress doesn't trigger when pressing back space.

HTML5 defines an oninput event to catch all direct changes. it works for me.

I encountered issues where Safari wasn't firing "onchange" events on a text input field. I used a jQuery 1.7.2 "change" event and it didn't work either. I ended up using ZURB's textchange event. It works with mouseevents and can fire without leaving the field:
http://www.zurb.com/playground/jquery-text-change-custom-event

$('.inputClassToBind').bind('textchange', function (event, previousText) {
    alert($(this).attr('id'));
});

try onpropertychange. it only works for IE.

It is better to use onchange(event) with <select>. With <input> you can use below event:

- onkeyup(event)
- onkeydown(event)
- onkeypress(event)

Checking for keystrokes is only a partial solution, because it's possible to change the contents of an input field using mouse clicks. If you right-click into a text field you'll have cut and paste options that you can use to change the value without making a keystroke. Likewise, if autocomplete is enabled then you can left-click into a field and get a dropdown of previously entered text, and you can select from among your choices using a mouse click. Keystroke trapping will not detect either of these types of changes.

Sadly, there is no "onchange" event that reports changes immediately, at least as far as I know. But there is a solution that works for all cases: set up a timing event using setInterval().

Let's say that your input field has an id and name of "city":

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

Have a global variable named "city":

var city = "";

Add this to your page initialization:

setInterval(lookForCityChange, 100);

Then define a lookForCityChange() function:

function lookForCityChange()
{
    var newCity = document.getElementById("city").value;
    if (newCity != city) {
        city = newCity;
        doSomething(city);     // do whatever you need to do
    }
}

In this example, the value of "city" is checked every 100 milliseconds, which you can adjust according to your needs. If you like, use an anonymous function instead of defining lookForCityChange(). Be aware that your code or even the browser might provide an initial value for the input field so you might be notified of a "change" before the user does anything; adjust your code as necessary.

If the idea of a timing event going off every tenth of a second seems ungainly, you can initiate the timer when the input field receives the focus and terminate it (with clearInterval()) upon a blur. I don't think it's possible to change the value of an input field without its receiving the focus, so turning the timer on and off in this fashion should be safe.

onchange only occurs when the change to the input element is committed by the user, most of the time this is when the element loses focus.

if you want your function to fire everytime the element value changes you should use the oninput event - this is better than the key up/down events as the value can be changed with the user's mouse ie pasted in, or auto-fill etc

Read more about the change event here

Read more about the input event here

use following events instead of "onchange"

- onkeyup(event)
- onkeydown(event)
- onkeypress(event)

A couple of comments that IMO are important:

• input elements not not emitting 'change' event until USER action ENTER or blur await IS the correct behavior.

• The event you want to use is "input" ("oninput"). Here is well demonstrated the different between the two: https://javascript.info/events-change-input

• The two events signal two different user gestures/moments ("input" event means user is writing or navigating a select list options, but still didn't confirm the change. "change" means user did changed the value (with an enter or blur our)

• Listening for key events like many here recommended is a bad practice in this case. (like people modifying the default behavior of ENTER on inputs)...

• jQuery has nothing to do with this. This is all in HTML standard.

• If you have problems understanding WHY this is the correct behavior, perhaps is helpful, as experiment, use your text editor or browser without a mouse/pad, just a keyboard.

My two cents.