jQuery / Ajax: How to pass JS variable to specific PHP function [closed] - php

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I am new to PHP and never used Ajax before so I hope someone can help me with this.
I have a separate functions.js file that stores all the JS I use for the pages of a website.
So far all the exchange with the db is done with PHP directly on the pages which works fine so far but now I have a scenario where I need to initiate this from the JS file.
My thought was I could create a separate PHP file (ajax.php) that hosts functions just for such purposes and then pass data via Ajax from the JS file to this PHP file.
So far I have the following but since there are multiple functions on the ajax.php file I am not sure how to pass this to the specific function I need.
Also, I am not sure if the Ajax call I have is set up correctly.
Can someone help me with this and maybe also explain your answer in a few words ?
Basically, here I want to pass the JS variable "itemID" to the PHP function fetchTransMain where this should be used for the variable $itemID (the variable $trans is generated in PHP).
Update: I would also need to know how to get the result from the PHP function back in JS. I didn't find an approach for this yet, perhaps with an Ajax GET call ??
What I have in my functions.js file:
var itemID = "someID";
$.ajax({
url: "ajax.php",
type: "post",
cache: "false",
data: itemID,
success: function(){
alert("success");
},
error: function(){
alert("failure");
}
});
...and on my ajax.php file:
function fetchTransMain($trans, $itemID){
foreach($trans as $key => $val){
if($val["ID"] == $itemID){
echo $val["trans"];
}
}
}
Many thanks in advance,
Mike

Answer 1

You have to define data as an object:
$.ajax({
url: "ajax.php",
type: "post",
cache: "false",
data: {itemId: itemID},
success: function(data) {
console.log(data);
alert("success");
},
error: function(){
alert("failure");
}
});
And then:
$itemId = $_POST['itemId'];
function fetchTransMain($trans, $itemID){
foreach($trans as $key => $val){
if($val["ID"] == $itemID){
echo $val["trans"];
}
}
}

Answer 2

I strongly suggest you to read some tutorial about ajax and PHP because there are so many aspects involved in this question that we can't explain them all in one answer. Anyway what you want to do is very common, you have a value in your browser that you want to save on your server.
The first part is almost correct:
$.ajax({
url: "ajax.php",
type: "post",
cache: "false",
data: {valueName: itemID},
success: function(){
alert("success");
},
error: function(){
alert("failure");
}
});
Just pay attantion to the data parameter, you should pass an object there with a name. That name is the name that you'll use on PHP to retrieve the value.
Then on server side:
function fetchTransMain($trans, $itemID){
foreach($trans as $key => $val){
if($val["ID"] == $itemID){
echo $val["trans"];
}
}
}
$valueFromClient = $_POST['valueName'];
fetchTransMain($trans, $valueFromClient);
Here you have to use $_POST since we have choose type: "post" on the client side.
Hope this helps