It is because you're only creating two td elements and 2 text nodes.

Creating all nodes in a loop

Recreate the nodes inside your loop:

var tablearea = document.getElementById('tablearea'),
    table = document.createElement('table');

for (var i = 1; i < 4; i++) {
    var tr = document.createElement('tr');

    tr.appendChild( document.createElement('td') );
    tr.appendChild( document.createElement('td') );

    tr.cells[0].appendChild( document.createTextNode('Text1') )
    tr.cells[1].appendChild( document.createTextNode('Text2') );

    table.appendChild(tr);
}

tablearea.appendChild(table);

Creating then cloning in a loop

Create them beforehand, and clone them inside the loop:

var tablearea = document.getElementById('tablearea'),
    table = document.createElement('table'),
    tr = document.createElement('tr');

tr.appendChild( document.createElement('td') );
tr.appendChild( document.createElement('td') );

tr.cells[0].appendChild( document.createTextNode('Text1') )
tr.cells[1].appendChild( document.createTextNode('Text2') );

for (var i = 1; i < 4; i++) {
    table.appendChild(tr.cloneNode( true ));
}

tablearea.appendChild(table);

Table factory with text string

Make a table factory:

function populateTable(table, rows, cells, content) {
    if (!table) table = document.createElement('table');
    for (var i = 0; i < rows; ++i) {
        var row = document.createElement('tr');
        for (var j = 0; j < cells; ++j) {
            row.appendChild(document.createElement('td'));
            row.cells[j].appendChild(document.createTextNode(content + (j + 1)));
        }
        table.appendChild(row);
    }
    return table;
}

And use it like this:

document.getElementById('tablearea')
        .appendChild( populateTable(null, 3, 2, "Text") );

Table factory with text string or callback

The factory could easily be modified to accept a function as well for the fourth argument in order to populate the content of each cell in a more dynamic manner.

function populateTable(table, rows, cells, content) {
    var is_func = (typeof content === 'function');
    if (!table) table = document.createElement('table');
    for (var i = 0; i < rows; ++i) {
        var row = document.createElement('tr');
        for (var j = 0; j < cells; ++j) {
            row.appendChild(document.createElement('td'));
            var text = !is_func ? (content + '') : content(table, i, j);
            row.cells[j].appendChild(document.createTextNode(text));
        }
        table.appendChild(row);
    }
    return table;
}

Used like this:

document.getElementById('tablearea')
        .appendChild(populateTable(null, 3, 2, function(t, r, c) {
                        return ' row: ' + r + ', cell: ' + c;
                     })
        );

var table = [["a1","a2","a3"]["b1","b2","b3"]["c1","c2","c3"]];
for(x = table.length;x > 0;x--) {
  document.write("<tr>");
  for(y = table[x].length;y > 0;y--) {
    document.write("<td>"+y+"</td>");
  }
document.write("</tr>");
}

Sorry if the syntax is wrong. You get the idea.

tr = tbl.getElementsByTagName("tr"); is an array of elements.So use tr[i] instead of tr inside for loop.

tbl = document.getElementsByTagName("body")[0];
  tr = tbl.getElementsByTagName("tr");
  for (i = 0; i < tr.length; i++) {

  var td = document.createElement('td');
  var input = document.createElement('INPUT');
  input.type = 'checkbox';
  td.appendChild(input);
  tr[i].appendChild(td);
}

<table border="1">
        <tr>
            <th>Email_id</th>
            <th>Email_content</th>
        </tr>
        <tr>
            <td>[email protected]</td>
            <td>bla bla</td>
        </tr>
        <tr>
            <td>[email protected]</td>
            <td>bla bla</td>
        </tr>
    </table>

You can add an input and a button to trigger the function. You could also check if the inserted value is actually a number or not.

$(document).on('click', '#add', function() {
  var that = $(this);
  var times = parseInt($('#times').val());
  for (i=1;i<=times;i++) {
    $('#table-wrp').append('<table class="table-times"><tbody><tr><td><img src="http://code52.org/aspnet-internationalization/icon.png" /></td></tr><tr><td>' + i + '</td></tr></tbody></table>');
  }
});

$(document).on('input', '#times', function() {
  var that = $(this);
  var value = that.val(); 
  if ((value != '' || value != false) && !isNaN(value)) {
    $('#add').prop('disabled', false);         
  } else {
    $('#add').prop('disabled', true);
  }      
});

#table-wrp {
  height: 80px;
}

.table-times {
  width: 100px;
  height: 80px;
  float: left;
  border-collapse: collapse;
}

.table-times td { 
   border: 1px solid #d8d8d8; 
   text-align: center;
 }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<input type="textbox" id="times" />
<button id="add" disabled>Add</button>
<div id="table-wrp"></div>