JSONP is a method for sending JSON data without worrying about cross-domain issues.
JSONP does not use the
XMLHttpRequestobject.JSONP uses the
<script>tag instead.
JSONP Intro #
JSONP stands for JSON with Padding.
Requesting a file from another domain can cause problems, due to cross-domain policy.
Requesting an external script from another domain does not have this problem.
JSONP uses this advantage, and request files using the script tag instead of the XMLHttpRequest object.
<script src="demo_jsonp.php">
<?php
$myJSON = '{ "name":"John", "age":30, "city":"New York" }';
echo "myFunc(".$myJSON.");";
?> The result returns a call to a function named “myFunc” with the JSON data as a parameter.
Make sure that the function exists on the client.
function myFunc(myObj) {
document.getElementById("demo").innerHTML = myObj.name;
} Creating a Dynamic Script Tag #
The example above will execute the “myFunc” function when the page is loading, based on where you put the script tag, which is not very satisfying.
The script tag should only be created when needed:
Example #
Create and insert the <script> tag when a button is clicked:
function clickButton() {
var s = document.createElement("script");
s.src = "demo_jsonp.php";
document.body.appendChild(s);
} <?php
header("Content-Type: application/json; charset=UTF-8");
$obj = json_decode($_GET["x"], false);
$conn = new mysqli("myServer", "myUser", "myPassword", "Northwind");
$result = $conn->query("SELECT name FROM ".$obj->$table." LIMIT ".$obj->$limit);
$outp = array();
$outp = $result->fetch_all(MYSQLI_ASSOC);
echo "myFunc(".json_encode($outp).")";
?> PHP File explained: #
- Convert the request into an object, using the PHP function json_decode().
- Access the database, and fill an array with the requested data.
- Add the array to an object.
- Convert the array into JSON using the json_encode() function.
- Wrap “myFunc()” around the return object.
JavaScript Example #
The “myFunc” function will be called from the php file:
function clickButton() {
var obj, s
obj = { table: "products", limit: 10 };
s = document.createElement("script");
s.src = "jsonp_demo_db.php?x=" + JSON.stringify(obj);
document.body.appendChild(s);
}
function myFunc(myObj) {
var x, txt = "";
for (x in myObj) {
txt += myObj[x].name + "<br>";
}
document.getElementById("demo").innerHTML = txt;
} function clickButton() {
var s = document.createElement("script");
s.src = "jsonp_demo_db.php?callback=myDisplayFunction";
document.body.appendChild(s);
} 
