For loop if statement recognizes == but not < in Javascript

Question

I'm trying to create a script that will replace certain values in my table with other values. I generated a table in HTML that works fine. I want to replace the elements in the 4th column in each of the first 3 rows with the value 1/8".

var rows = document.getElementsByTagName('tr');

for (var i = 0; i < rows.length; i++) {
 var cells = rows[i].getElementsByTagName('td');
 if (i < 3) {
  cells[3].innerHTML = '1/8"';
 }
}

Using the above code does nothing for my table, however using the following code replaces the 4th element with my value

var rows = document.getElementsByTagName('tr');

for (var i = 0; i < rows.length; i++) {
 var cells = rows[i].getElementsByTagName('td');
 if (i == 3) {
 cells[3].innerHTML = '1/8"';
 }
}

Why does == work, but < does not? Are there easy ways to print out the outputs of the for loop so i can debug easier - Im new to coding. Thanks!

Edit: Here is the HTML I'm using, along with the CSS (which is probably not necessary)

HTML5:

<div class="eo_product_listing_table">
<table class="tableizer-table">
<thead>
  <tr class="tableizer-firstrow">

    <th>Item #</th>
    <th>Type</th>
    <th>Operting Temp.</th>
    <th>O.D.</th>
    <th>Length</th>
    <th>Material</th>
    <th>Junction</th>
    <th>Price</th>
    <th>Order</th>
  </tr>
</thead>

<tbody>
  <!--1/8-->
  <!--6-->
  <tr>
    <td>NB4-CAXL-14U-12-AAG</td>
    <td>K</td>
    <td>-270°C to 1372°C</br>–454°F to 2501°F</td>
    <td>3/8"</td>
    <td>6"</td>
    <td>316SS</td>
    <td>Grounded</td>
    <td>$51.00</td>
    <td><a href="/">Order</a></td>
  </tr>
  <tr>
    <td>NB4-CAXL-14U-12-AAU</td>
    <td>K</td>
    <td>-270°C to 1372°C</br>–454°F to 2501°F</td>
    <td>3/8"</td>
    <td>6"</td>
    <td>316SS</td>
    <td>Ungrounded</td>
    <td>$53.00</td>
    <td><a href="/">Order</a></td>
  </tr>
  <tr>
    <td>NB4-CAXL-14U-12-AAE</td>
    <td>K</td>
    <td>-270°C to 1372°C</br>–454°F to 2501°F</td>
    <td>3/8"</td>
    <td>6"</td>
    <td>316SS</td>
    <td>Exposed</td>
    <td>$51.00</td>
    <td><a href="/">Order</a></td>
  </tr>
  <!--12-->
  <tr>
    <td>NB4-CAXL-14U-12-ABG</td>
    <td>K</td>
    <td>-270°C to 1372°C</br>–454°F to 2501°F</td>
    <td>3/8"</td>
    <td>12"</td>
    <td>316SS</td>
    <td>Grounded</td>
    <td>$53.00</td>
    <td><a href="/">Order</a></td>
  </tr>
  <tr>
    <td>NB4-CAXL-14U-12-ABU</td>
    <td>K</td>
    <td>-270°C to 1372°C</br>–454°F to 2501°F</td>
    <td>3/8"</td>
    <td>12"</td>
    <td>316SS</td>
    <td>Ungrounded</td>
    <td>$55.00</td>
    <td><a href="/">Order</a></td>
  </tr>
  <tr>
    <td>NB4-CAXL-14U-12-ABE</td>
    <td>K</td>
    <td>-270°C to 1372°C</br>–454°F to 2501°F</td>
    <td>3/8"</td>
    <td>12"</td>
    <td>316SS</td>
    <td>Exposed</td>
    <td>$53.00</td>
    <td><a href="/">Order</a></td>
  </tr>
  <!--18-->
  <tr>
    <td>NB4-CAXL-14U-12-ACG</td>
    <td>K</td>
    <td>-270°C to 1372°C</br>–454°F to 2501°F</td>
    <td>1/8"</td>
    <td>18"</td>
    <td>316SS</td>
    <td>Grounded</td>
    <td>$57.00</td>
    <td><a href="/">Order</a></td>
  </tr>
  <tr>
    <td>NB4-CAXL-14U-12-ACU</td>
    <td>K</td>
    <td>-270°C to 1372°C</br>–454°F to 2501°F</td>
    <td>1/8"</td>
    <td>18"</td>
    <td>316SS</td>
    <td>Ungrounded</td>
    <td>$59.00</td>
    <td><a href="/">Order</a></td>
  </tr>
  <tr>
    <td>NB4-CAXL-14U-12-ACE</td>
    <td>K</td>
    <td>-270°C to 1372°C</br>–454°F to 2501°F</td>
    <td>1/8"</td>
    <td>18"</td>
    <td>316SS</td>
    <td>Exposed</td>
    <td>$57.00</td>
    <td><a href="/">Order</a></td>
  </tr>
</tbody>

CSS3

.eo_product_listing_table {}

.tableizer-table tr:nth-child(even) {
   background-color: #eee;
}

table.tableizer-table {
  font-size: 12px;
  border: 1px solid #CCC;
  font-family: Arial, Helvetica, sans-serif;
  color: black;
}

.tableizer-table td {
  padding: 4px;
  margin: 3px;
  border: 0px solid #CCC;
  text-align: left;
  color: black;
}

.tableizer-table th {
  background-color: #104E8B;
  color: #FFF;
  font-weight: bold;
  text-align: left;
}

.tableizer-firstrow {
  background-color: #000;
  color: whtie;
}

Answer 1

For the first three iterations of your loop ( i < 3 ) you are just setting the same cell's innerHTML to '1/8"' again and again and again.

Maybe you'd meant to do:

var rows = document.getElementsByTagName('tr');

for (var i = 0; i < rows.length; i++) {
  var cells = rows[i].getElementsByTagName('td');
  if (i < 3) {
    cells[i].innerHTML = '1/8"';
  }
}

Answer 2

You use your script for ALL <tr> tag's, just like @Luaan said - look into your HTML file. That's mean, you must count form 1, not form 0. Then everything works fine.

var rows = document.getElementsByTagName('tr');

for (var i = 1; i < rows.length; i++) {
 var cells = rows[i].getElementsByTagName('td');
 if (i < 4) {
 cells[3].innerHTML = '1/8"';
 }
}

Answer 3

Okay, now that you've posted your HTML, the error is in plain sight :) The first tr you find contains no td s whatsoever, so you get an unhandled error and the function breaks.

You need to only look for rows in the tbody , excluding any that might be in theader or tfooter . It's also generally a good idea to make only iterate through rows of a particular table, rather than all rows in the whole document. You could even give the specific tbody an id and access it directly, avoiding all those issues.