Get previous value of select option - php

Question

Is there a way to get the previous value of select option?
the previous value is Red
If i change it to green it will echo the selected color
How can i echo the previous color which is red?
this is my code : thanks :)
<form action="#" method="post">
<select name="Color">
<option value="Red">Red</option>
<option value="Green">Green</option>
<option value="Blue">Blue</option>
<option value="Pink">Pink</option>
<option value="Yellow">Yellow</option>
</select>
<input type="submit" name="submit" value="Get Selected Values" />
</form>
<?php
if(isset($_POST['submit'])){
$selected_val = $_POST['Color'];
echo "You have selected :" .$selected_val . "<p>";
echo "The previous value is :" ;
}
?>

Answer 1

Use hidden field to store current value. On form post, check if the current value is different than selected value show it.
Pro tip: Always encrypt your hidden field data

Answer 2

store the previous value in your form as hidden value and get it
<?php
if(isset($_POST['submit'])){
$selected_val = $_POST['Color'];
$previous = $_POST['previous'];
}
?>
<form action="#" method="post">
<select name="Color">
<option value="Red">Red</option>
<option value="Green">Green</option>
<option value="Blue">Blue</option>
<option value="Pink">Pink</option>
<option value="Yellow">Yellow</option>
</select>
<input type="hidden" name="previous" value="<?php echo $selected_val; ?>"/>
<input type="submit" name="submit" value="Get Selected Values" />
</form>
<?php echo "You have selected :" .$selected_val . "<p>";
echo "The previous value is :".$previous ; ?>

Answer 3

Since you must never trust user submitted content, another way is to build your form from PHP and do the test on the server side.
Example:
<?php
$colors = Array('Red', 'Green', 'Blue', 'Pink', 'Yellow');
?>
<form method="POST">
<select name="Color"><?php
foreach($colors as $color)
{
printf(' <option value="%1$s">%1$s</option>'."\n", $color);
}
?>
</select>
<input type="submit">
</form>
<?php
if (!empty($_POST['Color']))
{
$previous_index = array_search($_POST['Color'], $colors) - 1;
// wrap around if the color is the first
if ($previous_index < 0) {
$previous_index = count($colors);
}
printf(
"You have selected <q>%s</q>, the previous value is: %s\n",
$_POST['Color'],
$colors[ $previous_index ]
);
}
?>
The code is obviously longer than it could for educative purpose.

Answer 4

Here is another solution using jQuery, as a bonus you keep track of whole history and not just previous selection.
I have not tested the PHP part, but you get the idea.
HTML
<form action="#" method="post">
<select name="Color" onChange="updateHistory(this);">
<option value="Red">Red</option>
<option value="Green">Green</option>
<option value="Blue">Blue</option>
<option value="Pink">Pink</option>
<option value="Yellow">Yellow</option>
</select>
<input type="hidden" id="history" name="history" value="">
</div>
</div>
<input type="submit" name="submit" value="Get Selected Values" />
</form>
<?php
if(isset($_POST['submit'])){
$selected_val = $_POST['Color'];
$hist = explode(',',$_POST['history']);
// pop the last value, which is current selection
array_pop($hist);
// get the last value, which now is previous
$last_valaue = end($hist);
echo "You have selected :" .$selected_val . "<p>";
echo "The previous value is :" . $last_valaue ;
echo 'DEBUG:<br>';
var_dump($hist);
}
?>
JS
function updateHistory(el){
var val = $(el).val();
var hist = $('#history').val();
if (hist.length > 0) {hist += ','}
hist += val;
$('#history').val(hist);
}
Example JS Fiddle
UPDATE 1:
You can further manipulate history array in PHP to your needs, for example, if you need unique values, you can use array_unique() (http://php.net/manual/en/function.array-unique.php)