Develop Reference

How to get value from an input field in javascript?

I tried .value , .textContent , innerText .... But nothing worked....
Below is my html
var input = document.getElementById('input').value
var button = document.getElementById('submit')
button.addEventListener('click', () => {
console.log(input) /// Output is always blank
})
<div class="input-section">
<input type="text" id="input" placeholder="Enter the word">
<button id="submit">Find</button>
</div>

You need to read the value property when the event fires, not before it.
let input = document.getElementById('input');
let button = document.getElementById('submit');
button.addEventListener('click',()=>{
console.log(input.value);
})

The reason why it is blank is because, you're initializing the input variable with the initial value inside input, i.e. nothing.
When you click the button, you want the "current" value of input, which means that you'd have to find value on each button click.
Do it like this :
var button = document.getElementById('submit')
button.addEventListener('click', () => {
var input = document.getElementById('input').value;
console.log(input);
})
<div class="input-section">
<input type="text" id="input" placeholder="Enter the word">
<button id="submit">Find</button>
</div>

How to display rounded values in a form and show on focus the original values?

I have numeric values with many decimal places and the precision is required for other functions. I want to present the values in a form, so the user can change the values if necessary.
To increase the readability, I want to display the values rounded to 2 decimal places, but if the user clicks on an input field, the complete value should be presented. By doing this, the user can see the real value and adjust them better.
Example:
HTML
<button id="myBtn" onclick="fillForm()">Try it</button>
<form id="myForm" >
<fieldset>
<input type="text" id="myInput1" onchange="myFunction()" >
</fieldset>
</form>
JavasSript
<script>
//Example values that should be presented
var x = 3.14159265359;
function fillForm(){
document.getElementbyId("myInput1").value = x;
}
function myFunction(){
x = document.getElementbyId("myInput1");
}
</script>
The form input value should be " 3.14 " and if the user clicks in the field, the displayed value should be 3.14159265359.
Now the user can change the value and the new value has to be saved.
Because this is for a local 1 page website with no guaranty of internet connection, it would be an asset but not a requirement, to do it without an external script (jquery …).

you can use focus and blur event to mask/unmask you float, then simply store the original value in a data param, so you can use the same function to all input in your form ;)
function fillForm(inputId, val)
{
var element = document.querySelector('#'+inputId);
element.value = val;
mask(element);
}
function mask(element) {
element.setAttribute('data-unmasked',element.value);
element.value = parseFloat(element.value).toFixed(2);
}
function unmask(element) {
element.value = element.getAttribute('data-unmasked') || '';
}
<button onclick="fillForm('myInput1',3.156788)">Fill!</button>
<form id="myForm" >
<fieldset>
<input type="text" id="myInput1" onblur="mask(this)" onfocus="unmask(this)" >
</fieldset>
</form>
Edit: added "fillForm()" :)

Just use .toFixed(). It accepts one argument, an integer, and will display that many decimal points. Since Javascript primitives are immutable, your x variable will remain the same value. (also when getting/setting the value of an input use the .value property
function fillForm(){
document.getElementbyId("myInput1").value = x.toFixed(2);
}
If you need to save it you can store it in a new value
var displayX = x.toFixed(2)

Here is my solution. I hope you have other suggestions.
HTML
<form id="myForm" >
<fieldset>
<input type="text" id="myInput1" >
</fieldset>
</form>
<button id="myBtn" onclick="fill_form()">fill form</button>
JavasSript
<script>
var apple_pi = 10.574148541;
var id_form = document.getElementById("myForm");
//Event listener for form
id _form.addEventListener("focus", copy_input_placeh_to_val, true);
id _form.addEventListener("blur", round_input_2decimal, true);
id _form.addEventListener("change", copy_input_val_to_placeh, true);
// Replace input value with input placeholder value
function copy_input_placeh_to_val(event) {
event.target.value = event.target.placeholder;
}
// Rounds calling elemet value to 2 decimal places
function round_input_2decimal(event) {
var val = event.target.value
event.target.value = Number(val).toFixed(2);
}
// Replace input placeholder value with input value
function copy_input_val_to_placeh(event) {
event.target.placeholder = event.target.value;
}
// Fills input elements with value and placeholder value.
// While call of function input_id_str has to be a string ->
//fill_input_val_placeh("id", value) ;
function fill_input_val_placeh (input_id_str, val) {
var element_id = document.getElementById(input_id_str);
element_id.placeholder = val;
element_id.value = val.toFixed(2);
}
// Writes a value to a form input
function fill_form(){
fill_input_val_placeh("myInput1", apple_pi);
}
</script>
Here is an running example
https://www.w3schools.com/code/tryit.asp?filename=FLDAGSRT113G

Here is solution, I used focus and blur listeners without using jQuery.
I added an attribute to input named realData
document.getElementById("myInput1").addEventListener("focus", function() {
var realData = document.getElementById("myInput1").getAttribute("realData");
document.getElementById("myInput1").value = realData;
});
document.getElementById("myInput1").addEventListener("blur", function() {
var realData = Number(document.getElementById("myInput1").getAttribute("realData"));
document.getElementById("myInput1").value = realData.toFixed(2);
});
function fillForm(value) {
document.getElementById("myInput1").value = value.toFixed(2);
document.getElementById("myInput1").setAttribute("realData", value);
}
var x = 3.14159265359;
fillForm(x);
<button id="myBtn" onclick="fillForm()">Try it</button>
<form id="myForm" >
<fieldset>
<input type="text" id="myInput1" realData="" onchange="myFunction()" >
</fieldset>
</form>
jsfiddle : https://jsfiddle.net/mns0gp6L/1/

Actually there are some problems that needs to be fixed in your code:
You are redeclaring the x variable inside your myFunction function with var x =..., you just need to refer the already declared x without the var keyword.
Instead of using document.getElementById() in myFunction, pass this as a param in onchange="myFunction(this)" and get its value in the function.
Use parseFloat() to parse the value of your input to a float, and use .toFixed(2) to display it as 3.14.
This is the working code:
var x = 3.14159265359;
function fillForm() {
document.getElementById("myInput1").value = x.toFixed(2);
}
function myFunction(input) {
x = parseFloat(input.value);
}
To display the original number when you click on the input you need to use the onfocus event, take a look at the Demo.
Demo:
var x = 3.14159265359;
function fillForm() {
document.getElementById("myInput1").value = x.toFixed(2);
}
function focusIt(input){
input.value = x;
}
function myFunction(input) {
x = parseFloat(input.value);
}
<button id="myBtn" onclick="fillForm()">Try it</button>
<form id="myForm">
<fieldset>
<input type="text" id="myInput1" onchange="myFunction(this)" onfocus="focusIt(this)">
</fieldset>
</form>

i have code it can be sum two textbox values using javascript

i have code it can be sum two textbox values using javascript but problem is that when i entered amount into recamt textbox value and javascript count again and again recamt textbox values it should be count only one time recamt textbox value not again and again?
<script type="text/javascript">
function B(){
document.getElementById('advance').value
=(parseFloat(document.getElementById('advance').value))+
(parseFloat(document.getElementById('recamt').value));
return false;
}
</script>
<input class="input_field2" type="text" readonly name="advance"
id="advance" value="50" onfocus="return B(0);" /><br />
<input class="input_field2" type="text" name="recamt" id="recamt">

You could keep a property on the read-only text field to keep the old value:
function B()
{
var adv = document.getElementById('advance'),
rec = document.getElementById('recamt');
if (typeof adv.oldvalue === 'undefined') {
adv.oldvalue = parseFloat(adv.value); // keep old value
}
adv.value = adv.oldvalue + parseFloat(rec.value));
rec.value = '';
return false;
}

You're calling the sum function every time the readonly input is focused using the new value. If you only want it to add to the original value, you need to store it somewhere.
HTML:
<input type="text" id="advance" readonly="readonly" value="50" /><br />
<input type="text" id="recamt">
JS:
var advanceBox = document.getElementById('advance');
var originalValue = advanceBox.value;
advanceBox.onclick = function() {
this.value = parseFloat(originalValue) +
parseFloat(document.getElementById('recamt').value);
return false;
};
http://jsfiddle.net/hQbhq/
Notes:
You should bind your handlers in javascript, not HTML.
The javascript would need to exist after the HTML on the page, or inside of a window.load handler, otherwise it will not be able to find advanceBox.

Grabbing User Input

First name: <input type="text" name="firstname"></input>
<input type="submit" value="Submit" />
Let's say I have the simple form above. How would I grab what the user inputted in the First Name field in JS. I tried:
document.getElementsByTagName("input")[1].onclick = function() {
inputted = document.getElementsByTagName("input")[0].innerHTML;
}
But that doesn't work. How would I do this?

Use value for text inputs:
inputted = document.getElementsByTagName("input")[0].value;
Also make sure to add var keyword to your variables so that you don't create a global variable:
var inputted = document.getElementsByTagName("input")[0].value;
You should also not put closing </input> tag since it is self-closing tag:
<input type="text" name="firstname" />
By the way you can also get elements value using below syntax:
formName.elementName.value;
Or
document.forms['formName'].elementName.value;
In your case it would be:
var inputted = formName.firstname.value;
Or
var inputted = document.forms['formName'].firstname.value;
Replace formName with whatever name is of your <form> element.
Lastly you can also get element's value if you apply id to it:
<input type="text" name="firstname" id="firstname" />
and then use getElementById:
var inputted = document.getElementById('firstname');

var inputs=document.getElementsByTagName("input"),
i=inputs.length;
//
while(i--){
inputs[i].onclick=myClickEventHandler;
};
//
function myClickEventHandler(evt){
var myVal;
switch (this.name) {
case 'firstname':
myVal = this.value;
break;
};
};

If you are using a form, you could try something like this instead :
var input = document.forms["formName"]["fieldName"].value;
Else, make use of the .value attribute :
var input = document.getElementsByTagName("input")[0].value;

Fill data in input boxes automatically

I have four input boxes. If the user fills the first box and clicks a button then it should autofill the remaining input boxes with the value user input in the first box. Can it be done using javascript? Or I should say prefill the textboxes with the last data entered by the user?

On button click, call this function
function fillValuesInTextBoxes()
{
var text = document.getElementById("firsttextbox").value;
document.getElementById("secondtextbox").value = text;
document.getElementById("thirdtextbox").value = text;
document.getElementById("fourthtextbox").value = text;
}

Yes, it's possible. For example:
<form id="sampleForm">
<input type="text" id="fromInput" />
<input type="text" class="autofiller"/>
<input type="text" class="autofiller"/>
<input type="text" class="autofiller"/>
<input type="button"value="Fill" id="filler" >
<input type="button"value="Fill without jQuery" id="filler2" onClick="fillValuesNoJQuery()">
</form>
with the javascript
function fillValues() {
var value = $("#fromInput").val();
var fields= $(".autofiller");
fields.each(function (i) {
$(this).val(value);
});
}
$("#filler").click(fillValues);
assuming you have jQuery aviable.
You can see it working here: http://jsfiddle.net/ramsesoriginal/yYRkM/
Although I would like to note that you shouldn't include jQuery just for this functionality... if you already have it, it's great, but else just go with a:
fillValuesNoJQuery = function () {
var value = document.getElementById("fromInput").value;
var oForm = document.getElementById("sampleForm");
var i = 0;
while (el = oForm.elements[i++]) if (el.className == 'autofiller') el.value= value ;
}
You can see that in action too: http://jsfiddle.net/ramsesoriginal/yYRkM/

or if input:checkbox
document.getElementById("checkbox-identifier").checked=true; //or ="checked"