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How to know if an input is clicked and unclicked in Javascript

I'm trying to figure out how to know when an input is clicked and when it is unclicked. Let me explain:
When ever you want to type something on an input field, you click on the input box and when you don't want to type, you click somewhere else and the input field is disabled.
<input type='text'>
Here as you can see, when you click on it, the field is enabled, and when you click somewhere else other than the field, it disables.
I just want to know when the field is disabled/unclicked.

When you click on the input field focus event is fired. When you lose focus blur event is fired.
var elem = document.getElementById("fname")
elem.addEventListener("blur", myFunction);
function myFunction() {
alert("Input field lost focus.");
}
<input type="text" id="fname">

I believe you're just looking for onFocus.
<input type='text' onFocus={/* do something */} />
Read more about React events here.

Event listener "change" only works if focus is on object

I'm currently having a little struggle with this. The situation is the following. I have multiple input fields on a page
Input1 and Input2 influence the content of Input3.
Now I wan't an event handler being triggered if content of Input3 changes. I tried:
$('#div-xy').on('change', 'input', function(){console.log('input changed')});
But that only seems to work if the focus is also on Input3 which isn't the case as I'm typing in input2 or input3.
I also tried:
$('#div-xy').bind('DOMSubtreeModified', function(){console.log('CHANGE2')});
which sadly has the same effect. Do you maybe have an idea how to check for changes in Input3? Would appreciate the help.

The change event only triggers on user input, but can be triggered explicitly.
Since you are using jQuery:
$('#input2').change(()=>{
console.log('input 2 is changed');
$('#input3').val('some val');
$('#input3').change()
})
$('#input3').change(()=>{
console.log('input 3 is changed');
})

Try like this:
If you have many of these fields, rather than having a handler be bound to each one, you would get better performance by using a delegated event handler:
HTML:
<div id='parent'>
<input type="text" class="search-field" />
<input type="text" class="search-field" />
<select class="search-field" ><option>1</option><option>2</option></select>
<input type="radio" class="search-field" />
</div>
JS:
$('#parent').on('change', '.search-field', function() {
// validate all search field values
// display search results based on values
// if search results already shown, filter based on $(this).val()
console.log($(this).val());
});

Technically, the change event occurs when the value of an element has been changed BY THE USER. It won't occur on it's own if the value of input3 is changed through jquery or some other code. However you can trigger that in any other jquery function manually and if there is a definition of input.change() then it will be executed.

how to copy a text of span

I copy need the dynamic text of a spam that is generated by a slider that the user sets. It must be copied to a value of an input.
I tried that, and didnt work:
<h4>Valor do consórcio: <span class="slider-value quote-form-element valor-carro1" data-name="Valor | Automóvel" name="Valor" data-slider-id="consorcio-auto">R$ <span id="THAT_VALUE"></span></span>
</h4>
<div class="slider" data-slider-min="20000" data-slider-max="100000" data-slider-start="23192" data-slider-step="1000" data-slider-id="consorcio-auto"></div>
<h4>Seus dados:</h4>
<input type="hidden" id="THAT_FIELD" name="THAT_FIELD" value="" />
<h4>Seus dados:</h4>
<input type="hidden" id="valorcarro" name="valorcarro" value="" />
script
$(function(){
var valorcarro = $('#THAT_VALUE').html();
$('#THAT_FIELD').val(valorcarro);
});
example in this page in the button on menu "Simulação".
The script just does not copy because the value is generated later and the user can still change

You need to use an event to fire your code after the slider value has changed. This is how you do it with a bootstrap slider.
$('.slider').on('slideStop', function () {
var valorcarro = $('#THAT_VALUE').text();
$('#THAT_FIELD').val(valorcarro);
});

To get the text of an element, use text()
For example
$("span").text();

you can try this code.
jQuery(function(){
var valorcarro = jQuery('#THAT_VALUE').text();
jQuery('#THAT_FIELD').val(valorcarro);
});

Actually, #Pamblam's response is better than mine. I was assuming the .slider class was for regular range inputs, which fire the 'change' event when their value changes, but it looks like it is in fact a bootstrap slider, which fires the slideStop event instead. Regardless, the code here listens for a change in the slider value, and when it is triggered, takes the text from the #THAT_VALUE span (from op's code) and sets the value of the #THAT_FIELD field to whatever it is :
$(".slider").change(function(){
var valorcarro = $('#THAT_VALUE').text();
$('#THAT_FIELD').val(valorcarro);
});

How to set prefilled input field active with Jquery/javascript?

I'm using a calculator widget where I can enter random values into an inputfield and then the widget automatically calculates when clicking the "go"-button.
Now I want to insert/prefill the value into this input field, since the value which needs to be calculated comes from a server. The issue though is, that this input field apparently only reacts on keypress. I tried to do this:
$('input[name="value"][data-type-money]').val('150.000').focus();
and
$('input[name="value"][data-type-money]').val('150.000').select();
which prefills the input field with the desired value but when I click the "go" button the calculation fails as long I dont enter the value manually into the input field. So, in the end my solution does not work.
Does anyone know how I can solve this?

If data changes frequently you can also use the setInterval function:
<input name="value" data-type-money="money">
setInterval (function(){
var moneyValue = "150.000";
$('input[name="value"][data-type-money]').val(moneyValue);
},1000);
fiddle here: http://jsfiddle.net/85pbnnu1/
or you can just do:
$(document).ready(function(){
$('input[name="value"][data-type-money]').val('150.000').change();
});

Edit, Updated
the input field is -
and reacts only on keypress, I mean when value is entered manually
If input value property cannot be changed , try replacing the element in DOM with value set at html using .replaceWith()
$('input[name="value"][data-type-money]')
.replaceWith("<input name=value data-type-money type=text value=150.00 />")
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js">
</script>
<input name="value" data-type-money type="text" />

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.