Passing PHP variables back to JavaScript variables on original page as Ajax

Question

I have some Ajax which passes a javascript variable to getfirstvals.php which then does its thing with the DB and echos out a table of values depending on the javascript variable I input. I now want to pass back these PHP variables which are being echoed, back to the original page that the javascript is being sent from in order to convert them into javascript variables to do calculations on. I'm not sure how to do this.

Below is how it works so far.

A range "slider" to select the values:

echo "<input id='slider' type='range'
min=\"$vartime[0]\" max=\"$timemax\" value=\"$vartime[0]\" step='any' />
<span id='range'> </span>"

......

    selectslider.onchange=function changecolour(){ 
    showValue(selectslider.value)

.....

<script type="text/javascript">
function showValue(str) {
if (str == "") {
    document.getElementById("datatable").innerHTML = "";
    return;
}
if (window.XMLHttpRequest) { // code for IE7+, Firefox, Chrome, Opera, Safari
    xmlhttp = new XMLHttpRequest();
} else { // code for IE6, IE5
    xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange = function () {
    if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
        document.getElementById("datatable").innerHTML = xmlhttp.responseText;
    }
}
if (floorchoice!=0 && floorchoice!=1){
    if (floorchoice==2)
    {
    xmlhttp.open("GET", "getfirstvals.php?q=" + str, true);
    xmlhttp.send();

......

This sends "q" to getfirstvals.php which finds values matching q in th DB and echoes out all values in the same row as it. In this way, as q changes the echoed values change. As I mentioned above, I would like these values not only to be echoed, but to be passed back to javascript variables on the original page which can then be used for calculations. Below is what I mean by the values being echoed:

        echo "<td>" . $FFlrOpenPlanTemp . "&#8451</td>";
    echo "<td>" . $FFlrPCRoomTemp . "&#8451</td>";
    echo "<td>" . $FFlrStudyRm6Temp . "&#8451</td>";
    echo "<td>" . $FFlrStudyRm8Temp . "&#8451</td>";

Jeff Lambert · Accepted Answer · 2011-08-16 20:05:18Z

2

Take a look at JSON. PHP has a function: json_encode which will take a PHP data object (ie array, but doesn't have to be an array) and encode it in javascript object notion.

In your JS you can then evaluate (tip: do not use eval, modern browsers have json parsers) to get the JSON data into Javascript object.

Example

If I have the following array in PHP:

$array = array( "test1" => 1, "test2" => 2, 3, array( 4, 5, 6 ));

And I json_encode that array, I wind up with the following string:

{"test1":1,"test2":2,"0":3,"1":[4,5,6]}

This is what you return back to JS (aka, echo out). You can parse this via the native parsing function JSON.parse in Javascript:

var obj = JSON.parse(phpReturnStr);

Voila. You have an object in JS passed in from PHP.

edited Aug 16, 2011 at 20:05

answered Aug 16, 2011 at 19:47

Jeff Lambert

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7 Comments

Peter Over a year ago

So would this work? And do I put it on the original page? var FFlrPCRoomTemp = <?php echo json_encode($FFlrPCRoomTemp) ?>;

Jeff Lambert Over a year ago

Updated answer with a simple example, let me know if you still don't follow.

Peter Over a year ago

I'm just trying to figure out how to implement this in my code. After I echo out the variables in the table I can then do this: json_encode($FFlrPCRoomTemp); Then on my first page I can do this: var obj = JSON.parse($FFlrPCRoomTemp); Is this right?

Jeff Lambert Over a year ago

No. You echo nothing out in the PHP file except the encoded JSON. You can either (a) have your table structure present but empty and filled by JS, (b) fetch the table structure from a different PHP file, or (c) create the table structure with Javascript and fill it with the results of the AJAX Request.

Peter Over a year ago

I think what I am doing is (b), I mean I send the variable "q" from the first page to getfirstvals.php, this then creates the table and fills it according to whatever values are on the same row a "q" in the DB, which is a primary key. What I want to do is get these values back to the original page, where I then want to convert them to JS and work with them. Do you understand what I'm getting at? Sorry if I'm not making much sense, I'm new to this and very tired at the moment!

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ldiqual · Accepted Answer · 2011-08-16 19:46:15Z

1

First, you could use a Javascript library to make it simpler and cross-browser. Then, I'd suggest you to pass your variables from PHP to JS with json_encode(). Just take a minute to see how jQuery.getJSON works, and it will be a child's play.

answered Aug 16, 2011 at 19:46

ldiqual

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