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In the below code I want to get the index value of rs using its Id and want to get its position

<table>
<tr>
<td id="1">Adi</td>
<td id="2">Aman</td>
</tr>
</table>
In the above code, I want to know the position of Aman using its id

You can try something like this:
html:
<table id="myTable">
<tr>
<td id="1">Adi</td>
<td id="2">Aman</td>
</tr>
</table>
js:
function getIdFromTable(searchValue)
{
var t = document.getElementById("myTable");
var trs = t.getElementsByTagName("tr");
var tds = null;
for (var i=0; i<trs.length; i++)
{
tds = trs[i].getElementsByTagName("td");
for (var n=0; n<tds.length;n++)
{
if (tds[n].innerText === searchValue) {
return tds[n].id;
}
}
}
}
getIdFromTable('Aman'); // will return 2

Easiest way to find position by id would be using prevAll().length. Something like this:
function findPositionById(id){
return $('#mytable').find('#'+id).prevAll().length
}
console.log('Adi Position', findPositionById(1));
console.log('Aman Position', findPositionById(2));
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.4/jquery.min.js"></script>
<table id="mytable">
<tr>
<td id="1">Adi</td>
<td id="2">Aman</td>
</tr>
</table>

Sum table values based on grouping

I have the following table:
<table>
<tr>
<th>Category</th>
<th>Value</th>
</tr>
<tr>
<td class="cat1">cat1</td>
<td class="value">123</td>
</tr>
<tr>
<td class="cat2">cat2</td>
<td class="value">356</td>
</tr>
<tr>
<td class="cat1">cat1</td>
<td class="value">486</td>
</tr>
</table>
I need a way to add/sum all values grouped by category, ie: add/sum all values in cat1, then add/sum all values in cat2. For each group I will do something with the total.
So I was hoping for something like:
for each unique category:
sum values in category
do something with this category total
For cat1 the total would be 123 + 486. Cat2 would just be 356. And so on if there were more categories.
I would prefer a purely javascript solution, but JQuery will do if that's not possible.

If I understand you correctly, you do a repeat of each td:first-child (The category cell).
Create a total object. You can check if the category is exist in it for each cell. If so, add current value to the stored value. If not, insert new property to it.
Like this:
var total = {};
[].forEach.call(document.querySelectorAll('td:first-child'), function(td) {
var cat = td.getAttribute('class'),
val = parseInt(td.nextElementSibling.innerHTML);
if (total[cat]) {
total[cat] += val;
}
else {
total[cat] = val;
}
});
console.log(total);
<table>
<tr>
<th>Category</th>
<th>Value</th>
</tr>
<tr>
<td class="cat1">cat1</td>
<td class="value">123</td>
</tr>
<tr>
<td class="cat2">cat2</td>
<td class="value">356</td>
</tr>
<tr>
<td class="cat1">cat1</td>
<td class="value">486</td>
</tr>
</table>

Here's a simple approach using only javascript
//grab data
var allTR = document.getElementsByTagName('TR');
var result = {};
//cycle table rows
for(var i=0;i<allTR.length;i+2){
//read class and value object data
var class = allTR[i].getAttribute('class');
var value = allTR[i+1].innerText;
//check if exists and add, or just add
if(result[class])
result[class] += parseInt(value);
else
result[class] = parseInt(value);
}

You have to use getElementsByTagName("td"); to get all the <td> collection and then you need to loop through them to fetch their innerText property which later can be summed up to get the summation.
Here is the working Fiddle : https://jsfiddle.net/ftordw4L/1/
HTML
<table id="tbl1">
<tr>
<th>Category</th>
<th>Value</th>
</tr>
<tr>
<td class="cat1">cat1</td>
<td class="value">123</td>
</tr>
<tr>
<td class="cat2">cat2</td>
<td class="value">356</td>
</tr>
<tr>
<td class="cat1">cat1</td>
<td class="value">486</td>
</tr>
<tr>
<td class="total"><b>Total</b></td>
<td class="totalValue"></td>
</tr>
</table>
Javascript
var tds=document.getElementsByTagName("td");
var total=0;
for (var i = 0; i<tds.length; i++) {
if (tds[i].className == "value") {
if(total==0) {
total = parseInt(tds[i].innerText);
} else {
total = total + parseInt(tds[i].innerText);
}
}
}
document.getElementsByClassName('totalValue')[0].innerHTML = total;
Hope this helps!.

here is a solution with jQuery :) if you are interested. it's pretty straightforward
var sumCat1 = 0;
var sumCat2 = 0;
$(".cat1 + .value").each(function(){
sumCat1 += parseInt($(this).text());
})
$(".cat2 + .value").each(function(){
sumCat2 += parseInt($(this).text());
})
console.log(sumCat1)
console.log(sumCat2)
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<table>
<tr>
<th>Category</th>
<th>Value</th>
</tr>
<tr>
<td class="cat1">cat1</td>
<td class="value">123</td>
</tr>
<tr>
<td class="cat2">cat2</td>
<td class="value">356</td>
</tr>
<tr>
<td class="cat1">cat1</td>
<td class="value">486</td>
</tr>
</table>

A simple approach in JQuery...
var obj = {};
$('tr').each(function() {
$this = $(this)
if ($this.length) {
var cat = $(this).find("td").first().html();
var val = $(this).find("td").last().html();
if (cat) {
if (!obj[cat]) {
obj[cat] = parseInt(val);
} else {
obj[cat] += parseInt(val);
}
}
}
})
console.log(obj)

Hide rows in table B which already appear in table A

Using this code :
var table1 = $('#TableA').find('td:eq(1)').text();
var table2 = $("#TableB tr:gt(0)");
table2.each(function (i) {
var tds = $(this).children('td');
var type= +tds.eq(0).text();
var price = +tds.eq(1).text();
if (price == table1) {
var myTable = table2.filter(function () {
var tds = $(this).children('td');
})
myTable.add(this).hide()
}
})
My Html Page Structure
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<table id="TableA">
<tr>
<th>Type</th>
<th>Price</th>
<th>Quantity</th>
<th>Ref No</th>
</tr>
<tr>
<td>Mouse</td>
<td>50</td>
<td>6</td>
<td>#101255</td>
</tr>
<tr>
<td>Speaker</td>
<td>300</td>
<td>6</td>
<td>#21165</td>
</tr>
</table>
<table id="TableB">
<tr>
<th>Type</th>
<th>Price</th>
<th>Quantity</th>
<th>Ref No</th>
</tr>
<tr>
<td>Mouse</td>
<td>50</td>
<td>6</td>
<td>#101255</td>
</tr>
<tr>
<td>Speaker</td>
<td>300</td>
<td>6</td>
<td>#21165</td>
</tr>
<tr>
<td>Keyboard</td>
<td>150</td>
<td>7</td>
<td>#31234</td>
</tr>
</table>
</body>
</html>
"The second table in the images is the Table B"
My Table B changes from this :
Before
To this : After
Now my problem is, only one row is hidden. The row, where "speaker" is, is still displayed. I know that I must use a loop for this, but I don't where to implement the loop and how. I'm a newbie programmer and I know that I need more practice. Please Help Thank you in advance

<script type="text/javascript">
$('body').click(function(e){
var table1_tr = $('#TableA').find('tr'); <!--get the rows of first table-->
var table2 = $("#TableB tr:gt(0)");
table1_tr.each(function(i,e){ <!-- loop through rows of first table -->
var table1 = $(e).find('td:eq(1)').text();
table2.each(function (i) {
var tds = $(this).children('td');
var type= +tds.eq(0).text();
var price = +tds.eq(1).text();
if (price == table1) {
var myTable = table2.filter(function () {
var tds = $(this).children('td');
})
myTable.add(this).hide()
}
});
})
});
</script>
you are checking the text of price in the first row of first table with td text of all the rows of second table
I modified script to loop through rows of first table and check them with all rows of second table
Hope this helps

How to multiply the contents of table cells via js?

I want to multiply cells content (only numbers) and using javascript.
The result is to be displayed in cell X
<script type="text/javascript">
function zmiana(){
var x = document.getElementById("rowstawka");
x.getElementsByTagName('td')[1].innerHTML=document.getElementById('Stawka2').value;
var y = document.getElementById("rowgodziny");
y.getElementsByTagName('td')[1].innerHTML=document.getElementById('Godziny').value;
}
</script>
I'm using the above script to add content to cells in a table.
And here is the table:
<table id="tabela">
<tr id="rowstawka">
<td>Stawka</td>
<td>12</td>
</tr>
<tr id="rowgodziny">
<td>Godziny</td>
<td>50</td>
</tr>
<tr id="rowPensja">
<td>Pensja</td>
<td>-</td>
</tr>
<tr id="rowNetto">
<td>Pensja Netto</td>
<td>x</td>
</tr>
</table>

If you can change the html, try using classes to determine which cells contains a number to be calculated:
<table id="tabela">
<tr id="rowstawka">
<td>Stawka</td>
<td class="num">12</td>
</tr>
<tr id="rowgodziny">
<td>Godziny</td>
<td class="num">50</td>
</tr>
<tr id="rowPensja">
<td>Pensja</td>
<td>-</td>
</tr>
<tr id="rowNetto">
<td>Pensja Netto</td>
<td id="result">x</td>
</tr>
</table>
Then use this simple snippet to make the magic:
var numbers = document.querySelectorAll(".num");
var total = 1;
for (var i = 0; i < numbers.length; i++)
{
total*= Number(numbers[i].innerText);
}
document.getElementById("result").innerText = total;
Fiddle

Calculating the value of a table

I have got a table.
I have assigned a different value to each of the lines
<table id="number1">
<tr>
<td id="value1">My Table</td>
</tr>
</table>
<script>
window.onload = function() {
document.getElementById("value1").value = "100"
</script>
I need to be able to get a value for the table "number 1" by adding the different rows of the table through Javascript.

var x=document.getElementById("number1");
var y= x.rows[0].cells[0].innerHTML=100;
<table id="number1">
<tr>
<td id="value1">My Table</td>
</tr>
</table>

You can use jquery
for(i=1;i<100000;i++){
$("#value"+i).html(i);
}

Try this
var total=0;
var last =1000000;
for(var i=1;i<parseInt(last);i++){
var id ="value" + i;
var element= document.getElementById(id);
if(element!= null){
document.getElementById(id).innerHTML=i + "00";
total=parseInt(total)+parseInt(element.innerHTML);
}
else
i=last;
}
document.getElementById("result").innerHTML="sum is =" + total;
<table id="number1">
<tr>
<td id="value1">My Table value 1 </td>
<td id="value2">My Table value 2 </td>
</tr>
</table>
<div id="result"></div>