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Javascript getElementById based on ID formed using fixed name and input number

I am trying to create ID dynamically in the HTML object and use of getElementById() in my javascript to access the HTML input value based on the button I clicked and insert into their respective HTML Select list.
My HTML snippets:
<input type="text" id="addDesc1"><input type="button" value="Add" onclick="addDescText(1)">
<input type="text" id="addDesc2"><input type="button" value="Add" onclick="addDescText(2)">
....
....
<select id="desc1">....</select>
<select id="desc2">....</select>
My javascript snippets:
function addDescText(id) {
var descText = document.getElementById("addDesc".concat(id)).value;
var selList = document.getElementById("desc".concat(id));
....
....
some javascript to add the respective description to their respective select list
....
}

concat() is an array method, you can not use that on string. Simply use + to concatenate the parameter with the string.
Demo:
function addDescText(id) {
var descText = document.getElementById("addDesc"+id).value;
var selList = document.getElementById("desc"+id);
console.log(descText);
console.log(selList);
}
<input type="text" id="addDesc1"><input type="button" value="Add" onclick="addDescText(1)">
<input type="text" id="addDesc2"><input type="button" value="Add" onclick="addDescText(2)">
<select id="desc1">....</select>
<select id="desc2">....</select>

I would encourage you to make use of the event parameter that is passed to all event handlers (on-click-event in your case) and add that handler programmatically.
A possible solution would be
HTML
<input type="text" id="text1">
<input type="button" value="Add" class="add-desc-button" data-target="1">
JS
// get all buttons
let allButtons = document.querySelectorAll('.add-desc-button')
// add event handler
for (let i=0; i<allButtons.length; i++) {
allButtons[i].addEventHandler('click', addDescriptionHandler)
}
// event handler
function addDescriptionHandler(event) {
// retrieve the number you passed in before like this
let number = event.target.getAttribute('data-target')
// ... your code here
}

Display input value in a button

I have an input field and a button next to it, what i want to do is whatever i type in the input field then click on the button next to it, the result gets displayed in another button, here is what i tried so far:
function add_keyword() {
var keyword_value = (document.getElementById("keyword").value);
var result = keyword_value;
document.getElementById("btnresult").value = result;
}
#btnresult{
display: none;
}
<button type="button" class="btn btn-default" name="clickbtn" value="Add Keyword" onclick="add_keyword()">Add</button>
<div class="input-group">
<input type="text" class="form-control" id="keyword" name="keywordbox"/>
</div>
<button type="button" id="btnresult" class="btn btn-default">input value should be here</button>

https://jsfiddle.net/sheriffderek/p2LoLcv3/
I think this is what you are describing...
Some simplified markup
<div class="parent">
<input type='button' value='Add' rel='action' /><br>
<input type='text' rel='text-input' />
</div>
<ul class='button-list' rel='button-list'>
<!-- you need to put the buttons somewhere, right? -->
</ul>
jQuery was one of the tags, so I used it
// just caching some thing that will be reused (I like using rel)
var $parent = $('.parent'); // whatever - to keep some scope
var $addButton = $parent.find('[rel="action"]');
var $textInput = $parent.find('[rel="text-input"]');
var $buttonList = $('[rel="button-list"]');
$addButton.on('click', function() { // on click...
var currentInputValue = $textInput.val(); // get the value from input...
$buttonList.append('<li><button>' + currentInputValue + '</button></li>'); // append a new button...
$textInput.val(''); // clear input
});

You're almost there, you have to unhide the button you've hidden in the first place, and not set a value for a button, but rather the innerHTML property. Since a button doesn't hold a value, but displays the content between the tags as text.
I've commented my changes:
function add_keyword() {
var keyword_value = (document.getElementById("keyword").value);
var result = keyword_value;
// Changed from .value to .innerHTML
document.getElementById("btnresult").innerHTML = result;
// Changed style from to 'block'
document.getElementById("btnresult").style.display = "block"
}
#btnresult{
display: none;
}
<button type="button" class="btn btn-default" name="clickbtn" value="Add Keyword" onclick="add_keyword()">Add</button>
<div class="input-group">
<input type="text" class="form-control" id="keyword" name="keywordbox"/>
</div>
<button type="button" id="btnresult" class="btn btn-default">input value should be here</button>
In addition, there are several aspects of your code that could use improvement, I described them below:
function add_keyword() {
// No need for parentheses around the document.getElement function.
var keyword_value = document.getElementById("keyword").value;
// There's no need to place the value in a new variable, it is useful to place the element you wish to replace in a variable, since we'll be re-using it's instance.
var btn = document.getElementById("btnresult");
btn.innerHTML = keyword_value;
btn.style.display = "block"
}
EDIT: Since OP's goal was to create a new button with the content, this is an updated version that generates a new button for every new input.
function add_keyword() {
var keyword_value = document.getElementById("keyword").value;
// Create a new button element.
var btn = document.createElement("button");
// Set it's content to the keyword from the input.
btn.innerHTML = keyword_value
// Append it to the body.
document.body.appendChild(btn);
}
<button type="button" class="btn btn-default" name="clickbtn" value="Add Keyword" onclick="add_keyword()">Add</button>
<div class="input-group">
<input type="text" class="form-control" id="keyword" name="keywordbox"/>
</div>

how to update sub attributes in html custom button input via javascript

I want to update data-percent value on a radiobutton click before clicking the update button
html:
<input type="radio" name="percentage" value="50" onclick="changeVal(this.value)"> Happy 50 percent</input>
</br>
<input type="radio" name="percentage" value="75" onclick="changeVal(this.value)"> Happy 75 percent</input>
</br>
<button class="btn btn-danger my-btn" id = "myUpdateBtn" data-id="1" data-name="John" data-summary="John is Happy" data-percent="50" >Click to Update</button>
javascript: my script function does not update button sub attribute value. please help.
changeVal(val){
alert(val);
document.getElementById("myUpdateBtn").value('data-price') = val;
}

In order to access data attributes you have to do it like this:
var val = document.getElementById('21').dataset.id;
var msg = document.getElementById('21').dataset.name;
alert(val); //Alert '21'
alert(msg); //Alert 'HiDiv'
document.getElementById('21').dataset.lastName = 'Rod'; //Create new data attribute
console.log(document.getElementById('21')); //View changes
<div data-id='21' id='21' data-name = 'HiDiv'>
</div>

Getting hiddenvalue HTML property from javascript

I am trying to access the hidden HTML value (hiddenvalue) from javascript and storing it into a variable env.
HTML:
<button id="slct" hiddenfield="Forest" type="button" class="btn btn-default">Hello</button>
JS:
$('#slct').click(function (event) {
document.getElementById('env').value = $('#' + $(event.target).data('hiddenfield')).value;
});
What am I missing?

I would create a hidden html field
<input type="hidden" id="someId" value="someValue">
Getting the value of this field would look like:
var theValue = document.getElementById('someId').value;
What you want is probably this:
html:
<input type="hidden" id="env" value="">
<button class="slct" hiddenfield="Forest" type="button" class="btn btn-default">This sets Forest</button>
<button class="slct" hiddenfield="Fruit" type="button" class="btn btn-default">This sets Fruit</button>
javascript:
$('.slct').click(function(event) {
// Set value to hidden field
$('#env').val($(this).attr('hiddenfield'));
});
you can use data() instead of attr(), but the attribute needs to start with 'data-' then. E.g. data('hiddenvalue') to retrieve the value of attribute data-hiddenvalue
(see https://jsfiddle.net/2k0791hk/1/)

How to Remove last inserted div in javascript?

<div id="file">
<input type="file" name="txtImage" multiple="multiple" class="upload" />
<input type="text" name="txtImageDesc" class="desc" />
</div>
<input type="button" value="Add" name="addButton" onclick="javascript: add_more();" />
<input type="button" value="Remove" name="removeButton" onclick="javascript: remove();" />
The above is two button which add or remove div on its calls.I have a java script function which is adding a div in html on call which works perfect
function add_more()
{
var txt = " <p><label>Upload Image</label><input type=\"file\" name=\"txtImage[]\"></p> <p>
<label>Image Description</label><input type=\"text\" name=\"txtImageDesc[]\"> </p>";
document.getElementById("file").innerHTML += txt;
}
However i am using the same script(with modification) to remove the last inserted div in it but its removing the whole html in the div.Here is the code:
function remove() {
var txt = " <p><label>Upload Image</label><input type=\"file\" name=\"txtImage[]\"></p>
<p><label>Image Description</label><input type=\"text\" name=\"txtImageDesc[]\"> </p>";
document.getElementById("file").innerHTML -= txt;
}
The output it generate is.I want the last div inserted to be remove on button click
NaN

As already said in comments, you are adding p elements here, not div.
If you don’t want to use jQuery, you can do it in “pure JS” as well, like this:
function lastParagraphBeGone() { // brilliant function name :-)
var paragraphs = document.getElementById("file").getElementsByTagName("p");
var lastParagraph = paragraphs[paragraphs.length-1];
lastParagraph.parentNode.removeChild(lastParagraph);
}

$('#file p').slice(-2).remove(); will remove the last 2 P elements from your #file element:
LIVE DEMO
HTML:
<input type="button" value="Add" name="addButton" />
<input type="button" value="Remove" name="removeButton" />
<div id="file"></div>
jQ:
var html = " <p><label>Upload Image</label><input type=\"file\" name=\"txtImage[]\"></p><p><label>Image Description</label><input type=\"text\" name=\"txtImageDesc[]\"></p>";
$('[name=addButton]').click(function(){
$('#file').append( html );
});
$('[name=removeButton]').click(function(){
$('#file p').slice(-2).remove();
});
https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Array/slice

Javascript uses the same operator for concatenation and for addition; so adding works.
But the minus operator is only for subtraction. So you try to subtract text from text which aren't numbers, so it's a NaN.
You cannot remove by this way: Use some function to search the beginning of this string and extract it so or simply add an id attribute to your <p> tag, so you can simply hide it when not needed anymore.

This works for me. One thing that seems to break this kind of function is when the adding text is on separate lines. So, always put that kind of "txt" addition on a single line in javascript.
<script type="text/javascript" >
function add_more()
{
var txt = " <p><label>Upload Image</label><input type=\"file\" name=\"txtImage[]\"></p><p><label>Image Description</label><input type=\"text\" name=\"txtImageDesc[]\"> </p>";
document.getElementById("extra-text").innerHTML = txt;
}
function remove() {
document.getElementById("extra-text").innerHTML = '';
}
</script>
<input type="button" value="Add" name="addButton" onclick="javascript: add_more();" />
<input type="button" value="Remove" name="removeButton" onclick="javascript: remove();" />
<div id="file"><h1>Existing text</h1>
<div id="extra-text"></div>
</div>