I am working on a site which connects to a MySQL database and lets you display/edit the data in it. The site uses JavaScript and PHP, with HTML and CSS parts (these are added using JS).
The site works, does everything I wanted it to do, but only from PC. When I try to use it from a smartphone, some of the hidden fields' value doesn't get submitted correctly to the PHP page responsible to working with them.
First, I have a few of this select box:
var maxLvl;
var select = document.createElement( 'select' );
var trooplist = [archerLvl, giantLvl, wizardLvl, balloonLvl, dragonLvl]; //this array contains numbers, which will be used to set the starting option in the select
select.id = "select" + k + " " + i; //k and i are both variables in their respective for loop: k goes from 0 to 2, in it there's another with i.
select.onblur = function() {
var selectid = this.id;
var last = selectid.slice(-1);
if(last==0){
document.getElementById("hiddenArcherid").value = this.value;
alert(document.getElementById("hiddenArcherid").name + " " + document.getElementById("hiddenArcherid").value);
}else if(last==1){
document.getElementById("hiddenGiant").value = this.value;
alert(document.getElementById("hiddenGiant").name + " " + document.getElementById("hiddenGiant").value);
}else if(last==2){
document.getElementById("hiddenWizard").value = this.value;
alert(document.getElementById("hiddenWizard").name + " " + document.getElementById("hiddenWizard").value);
}else if(last==3){
document.getElementById("hiddenBalloon").value = this.value;
alert(document.getElementById("hiddenBalloon").name + " " + document.getElementById("hiddenBalloon").value);
}else if(last==4){
document.getElementById("hiddenDragon").value = this.value;
alert(document.getElementById("hiddenDragon").name + " " + document.getElementById("hiddenDragon").value);
}
};
select.style.position = "absolute";
select.style.left = 250 + (i*(width + (width/10))) +"px";
select.style.top = 110 + height + (rowcounter * (height * 1.5)) + "px";
select.style.width = width;
if(i==0 || i==1 || i==2 || i==3)
maxLvl = 6;
else
maxLvl=4;
for(var l=0; l <= maxLvl; l++){
var option = document.createElement( 'option' );
option.setAttribute("value", l);
option.innerHTML = "Level " + l;
select.appendChild(option);
}
select.selectedIndex = trooplist[i];
IDarray.push(select.id);
document.body.appendChild(select);
This code runs in a for loop, and creates 5 select boxes using data passed by a function. Then, when the user selects a new option, the option's value is stored in a HTML hidden input field with. Like this one:
var hiddenArcher = document.createElement('input');
hiddenArcher.setAttribute("type","hidden");
hiddenArcher.name = "hiddenArcher";
hiddenArcher.id = "hiddenArcherid";
hiddenArcher.setAttribute("value", document.getElementById("select1 0").value);
formNew.appendChild(hiddenArcher);
These input fields have a basic value, which is the default of the select box - 0 if the user creates a new entry, or an already known value if the user wants to modify an already existing entry. All the input fields have the same structure, only the JS var, the name, the id and the default value changes.
The input fields are part of the formNew form, which has multiple submit buttons - pressing those buttons posts the fields' values to a PHP page, which executes the MySQL queries, depending on which button was pressed. For this, I use if/else if (isset). Then the PHP redirects (by using header("Location: http://my_sites_address"); exit();) to the main page - the one I where the select boxes are.
If I try it from Chrome, the site works - The right values get passed, the PHP executes the right queries correctly. I can add new entry, and both delete or modify existing ones. When I try it on Android (via emulator) or iOS (via my friend's phone), although I can select the values I want to change, and the alerts display the correct data, too, when I hit submit, nothing happens within the database, it seems like I did nothing. The browser gets redirected to the PHP, so I guess the submit does happen, but there will be no changes in the database. The PHP simply redirects to the main page, and that's all.
The only function can be used successfully on phone is deleting the entry, most likely because the hidden field responsible for storing the row's ID gets it's value the moment it's added to (a different) form, and the value never changes, only when the user switches to a different entry.
The hidden fields "physically" (based on their location in the file) are declared later than the select boxes.
Currently, the code acts this way on phone: 1) I start editing the entry. The select boxes show up. 2) I can select the desired value. 3) An alert pops up, confirming the value got passed to the hidden field. 4) I press the submit button, comes the PHP, then the redirects, and I am back where I started. There are no changes in the database.
I already tried to switch onchange to onblur at the select boxes; I made sure JS is enabled (which was totally unnecessary, because the images/texts displayed with JS). Right now I have no idea what's wrong.
Are any of you experienced something similar, or has any idea what should I do?
Some browsers fail to correctly and completely recognize the programmatic change of a hidden input's value immediately after it is changed. If you submit the form directly after changing the hidden input's value via javascript, the value sent for that input will be the pre-change value, rather than the value you set in javascript.
Unfortunately, I don't have a list of browsers that exhibit this behavior, nor do I know the exact mechanics behind it. What I do know is that I've run into the issue you're describing, and I have always been able to solve it by triggering a change event on the hidden input after changing its value via javascript.
For those using plain javascript with no external libraries, your code would look something like this (see here):
<input id="myHidden" name="myHidden" type="hidden" value="old value"/>
<script type="text/javascript">
var hiddenInput = document.getElementById('myHidden');
hiddenInput.value = 'new value';
console.log(hiddenInput.value); // = 'new value'
// Submit the form now, and myHidden='old value' will be sent to the server
// Set up and trigger the change event on our input:
var changeEvent = document.createEvent("UIEvents");
changeEvent.initUIEvent("change", true, true);
hiddenInput.dispatchEvent(changeEvent);
// Submit the form now, and myHidden='new value' will be sent to the server
</script>
For those using jQuery or a similar library, the code is a little more concise:
<input id="myHidden" name="myHidden" value="old value"/>
<script type="text/javascript">
var $hiddenInput = $('#myHidden');
$hiddenInput.val('new value');
console.log($hiddenInput.val()); // = 'new value'
// Submit the form now, and myHidden='old value' will be sent to the server
// Trigger the change event on our input:
$hiddenInput.change();
// Submit the form now, and myHidden='new value' will be sent to the server
</script>
Really concise example (one-liner) using jQuery:
<input id="myHidden" name="myHidden" value="old value"/>
<script type="text/javascript">
$('#myHidden').val('new value').change();
// Submit the form now, and myHidden='new value' will be sent to the server
</script>
Here's a working example using a slightly simplified version of the code supplied in the original question.