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How to preview the result of a beforeinput event?

Does the beforeinput event provide a convenient way to preview the result of a proposed modification so that it can be blocked if necessary for validation purposes?
I'm not looking for alternative ways to do input validation; I'm already well-aware of methods involving the keypress and input events, as well as HTML5 validation, etc.. Right now, I'm specifically looking into the beforeinput event to see what it offers.
So far, this is the best I've come up with:
document.getElementById("phone").addEventListener("beforeinput", function(e) {
if(!/^(\d{0,7}|\d{3}-\d{0,4}|)$/.test(e.target.value + (e.data ?? ""))) {
e.preventDefault();
}
return;
});
<input id="phone">
The text field in the above snippet should accept a simple 7-digit phone number with optional dash after the 3rd digit.
Notice that I'm appending the event's data property to the input's current value to create a preview of the modified value. This works fine if you only enter input sequentially. But if, for example, you type in all 7 digits and then arrow back to just after the 3rd and try to insert the dash, you can't do it, because the validation assumes you're at the end where a dash would be invalid. Other problems arise if you try to replace or delete a selection.
An accurate preview will be required to solve these problems. Is there a simple way to get one from the beforeinput event?

You'd have to get the selectionStart and selectionEnd to figure out how many characters were removed / replaced / etc, but yeah, pretty simple:
document.getElementById("phone").addEventListener("beforeinput", function(e) {
const nextVal =
e.target.value.substring(0, e.target.selectionStart) +
(e.data ?? '') +
e.target.value.substring(e.target.selectionEnd)
;
console.log(nextVal)
if(!/^(\d{0,7}|\d{3}-?\d{0,4}|)$/.test(nextVal)) {
e.preventDefault();
}
return;
});
<input id="phone">

Javascript - Display input inside div

So this is probably an easy one, but I'm just not doing it right. My goal is to send the user input from this textbox:
<input type='text' placeholder='Form Name...' id='formNameInput' required>
Into this Div:
<div id="code_output"></div>
I'm trying to make it appear in real time, and so far I used this to try and do so, but it doesn't work:
document.getElementById("code_output").innerHTML += document.getElementById("formNameInput").value;
Why doesn't it show? Does my code need something to trigger the Javascript?

You're close, but the issue is that you're not using an event handler. The script is executing your code once, as soon as possible (before you have the chance to enter anything into the text input). So, you have to add some sort of event listener so that the copying happens at the appropriate time. Something like below:
document.getElementById('formNameInput').addEventListener('keyup', copyToDiv);
function copyToDiv() {
document.getElementById("code_output").innerHTML = document.getElementById("formNameInput").value;
}
<input type='text' placeholder='Form Name...' id='formNameInput' required>
<div id="code_output"></div>

You need to do that whenever the value of formNameInput changes. For that you need an event.
Your code should look like:
document.getElementById("formNameInput").addEventListener('input', function () {
document.getElementById("code_output").innerHTML += this.value;
});

function change() {
document.getElementById("code_output").innerHTML = document.getElementById("formNameInput").value;
}
document.getElementById('formNameInput').onkeyup = change
maybe this is what you are trying?

You need to attach an event listener to your input that executes a function any time an input event occurs on the field:
formNameInput.addEventListener('input', function(e) {
code_output.textContent = e.target.value
})
<input type="text" placeholder="Form Name..." id="formNameInput" required />
<div id="code_output"></div>
Please note that the above code takes advantage of the fact that browsers automatically create a global variable for each element with a unique id attribute value, and this variable has the same name as the value of the id.
If the concept of events is new to you, this might be a good place to get started:
https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Building_blocks/Events

HTML5 Chrome checkValidity onBlur

I'm trying to do a simple checkValidity of a numeric input field on blur, but can't get it to work properly. Does this work in Chrome yet? For instance:
<input onBlur="checkValidity()" type="number" name="x" id="x" min="64" max="2048" value=64>
or
<input onBlur="this.checkValidity()" type="number" name="x" id="x" min="64" max="2048" value=64>
Don't seem to do anything. However, in the console,
$("#x")[0].checkValidity()
does return true or false based on the current value in the input box and the limits above of (64,2048). Is this broken, or am I doing it wrong?

I realize this question is many years old at this point but if anyone else comes across it, the correct way to achieve the behavior that OP wanted appears to be to use onblur="reportValidity()" instead onblur="checkValidity".

This is a demonstration of what you may want to head to:
http://jsfiddle.net/9gSZS/
<input type="number" min="64" max="256" onblur="validate(this);" />
function validate(obj)
{
if(!obj.checkValidity())
{
alert("You have invalid input. Correct it!");
obj.focus();
}
}
Noted that I'm just demonstrating the concept here; alert may cause very unpleasant experience, so don't just copy it.
Use some floating DIV to attract your user, instead of the full-blocking alert.

You should use onChange Event
for example
var input1 = document.getElementById('txt_username');
input1.onchange = function(){
input1.setCustomValidity(input1.validity.patternMismatch ? 'username must match a-z,A-Z,0-9,4-16 character' : '');
}

Here is a solution
$("form").focusout(function(){
if(!$("form")[0].checkValidity()){
setTimeout(function(){$(":submit").eq(0).trigger('click');},0);
}
});
If any of your form elements lose focus you check the form validity. If the form is invalid have jquery click the first submit button. Have to use a timeout for some reason to get it to work. A timeout of zero just moves the function to the end of the queue of functions.

onblur="checkValidity()" has no effect because blur event is not cancelable.

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);
}

onchange is only triggered when the control is blurred. Try onkeypress instead.

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/

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

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)

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);
}

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'));
});

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.

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

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

when we use onchange while you are typing in input field – there’s no event. But when you move the focus somewhere else, for instance, click on a button – there will be a change event
you can use oninput
The oninput event triggers every time after a value is modified by the user.Unlike keyboard events, it triggers on any value change, even those that does not involve keyboard actions: pasting with a mouse or using speech recognition to dictate the text.
<input type="text" id="input"> oninput: <span id="result"></span>
<script>
input.oninput = function() {
console.log(input.value);
};
</script>
If we want to handle every modification of an <input> then this event is the best choice.

I have been facing the same issue until I figured out how to do it. You can utilize a React hook, useEffect, to write a JS function that will trigger after React rendering.
useEffect(()=>{
document.title='fix onChange with onkeyup';
const box = document.getElementById('changeBox');
box.onkeyup = function () {
console.log(box.value);
}
},[]);
Note onchange is not fired when the value of an input is changed. It is only changed when the input’s value is changed and then the input is blurred. What you’ll need to do is capture the keypress event when fired in the given input and that's why we have used onkeyup menthod.
In the functional component where you have the <Input/> for the <form/>write this
<form onSubmit={handleLogin} method='POST'>
<input
aria-label= 'Enter Email Address'
type='text'
placeholder='Email Address'
className='text-sm text-gray-base w-full mr-3 py-5 px-4 h-2 border border-gray-primary rounded mb-2'
id='changeBox'
/>
</form>
Resulting Image :
Console Image

try onpropertychange.
it only works for IE.

Clear default values using onsubmit

I need to clear the default values from input fields using js, but all of my attempts so far have failed to target and clear the fields. I was hoping to use onSubmit to excute a function to clear all default values (if the user has not changed them) before the form is submitted.
<form method='get' class='custom_search widget custom_search_custom_fields__search' onSubmit='clearDefaults' action='http://www.example.com' >
<input name='cs-Price-2' id='cs-Price-2' class='short_form' value='Min. Price' />
<input name='cs-Price-3' id='cs-Price-3' class='short_form' value='Max Price' />
<input type='submit' name='search' class='formbutton' value=''/>
</form>
How would you accomplish this?

Read the ids+values of all your fields when the page first loads (using something like jquery to get all "textarea", "input" and "select" tags for example)
On submit, compare the now contained values to what you stored on loading the page
Replace the ones that have not changed with empty values
If it's still unclear, describe where you're getting stuck and I'll describe more in depth.
Edit: Adding some code, using jQuery. It's only for the textarea-tag and it doesn't respond to the actual events, but hopefully it explains the idea further:
// Keep default values here
var defaults = {};
// Run something like this on load
$('textarea').each(function(i, e) {
defaults[$(e).attr('id')] = $(e).text();
});
// Run something like this before submit
$('textarea').each(function(i, e){
if (defaults[$(e).attr('id')] === $(e).text())
$(e).text('');
})
Edit: Adding some more code for more detailed help. This should be somewhat complete code (with a quality disclaimer since I'm by no means a jQuery expert) and just requires to be included on your page. Nothing else has to be done, except giving all your input tags unique ids and type="text" (but they should have that anyway):
$(document).ready(function(){
// Default values will live here
var defaults = {};
// This reads and stores all text input defaults for later use
$('input[type=text]').each(function(){
defaults[$(this).attr('id')] = $(this).text();
});
// For each of your submit buttons,
// add an event handler for the submit event
// that finds all text inputs and clears the ones not changed
$('input[type=submit]').each(function(){
$(this).submit(function(){
$('input[type=text]').each(function(){
if (defaults[$(this).attr('id')] === $(this).text())
$(this).text('');
});
});
});
});
If this still doesn't make any sense, you should read some tutorials about jQuery and/or javascript.

Note: This is currently only supported in Google Chrome and Safari. I do not expect this to be a satisfactory answer to your problem, but I think it should be noted how this problem can be tackled in HTML 5.
HTML 5 introduced the placeholder attribute, which does not get submitted unless it was replaced:
<form>
<input name="q" placeholder="Search Bookmarks and History">
<input type="submit" value="Search">
</form>
Further reading:
DiveintoHTML5.ep.io: Live Example... And checking if the placeholder tag is supported
DiveintoHTML5.ep.io: Placeholder text

1) Instead of checking for changes on the client side you can check for the changes on the client side.
In the Page_Init function you will have values stored in the viewstate & the values in the text fields or whichever controls you are using.
You can compare the values and if they are not equal then set the Text to blank.
2) May I ask, what functionality are you trying to achieve ?

U can achieve it by using this in your submit function
function clearDefaults()
{
if(document.getElementById('cs-Price-2').value=="Min. Price")
{
document.getElementById('cs-Price-2').value='';
}
}