Zilliqa/SmartContract

he PHP File

PHP has some built-in functions to handle JSON.

Objects in PHP can be converted into JSON by using the PHP function json_encode():
PHP file
<?php
$myObj->name = "John";
$myObj->age = 30;
$myObj->city = "New York";

$myJSON = json_encode($myObj);

echo $myJSON;
?>
The Client JavaScript

Here is a JavaScript on the client, using an AJAX call to request the PHP file from the example above:
Example

Use JSON.parse() to convert the result into a JavaScript object:
var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
var myObj = JSON.parse(this.responseText);
document.getElementById("demo").innerHTML = myObj.name;
}
};
xmlhttp.open("GET", "demo_file.php", true);
xmlhttp.send();
PHP Array

Arrays in PHP will also be converted into JSON when using the PHP function json_encode():
PHP file
<?php
$myArr = array("John", "Mary", "Peter", "Sally");

$myJSON = json_encode($myArr);

echo $myJSON;
?>
The Client JavaScript

Here is a JavaScript on the client, using an AJAX call to request the PHP file from the array example above:
Example

Use JSON.parse() to convert the result into a JavaScript array:
var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
var myObj = JSON.parse(this.responseText);
document.getElementById("demo").innerHTML = myObj[2];
}
};
xmlhttp.open("GET", "demo_file_array.php", true);
xmlhttp.send();
PHP Database

PHP is a server side programming language, and can be used to access a database.

Imagine you have a database on your server, and you want to send a request to it from the client where you ask for the 10 first rows in a table called "customers".

On the client, make a JSON object that describes the name of the table, and the numbers of rows you want to return.

Before you send the request to the server, convert the JSON object into a string and send it as a parameter to the url of the PHP page:
Example

Use JSON.stringify() to convert the JavaScript object into JSON:
obj = { "table":"customers", "limit":10 };
dbParam = JSON.stringify(obj);
xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
document.getElementById("demo").innerHTML = this.responseText;
}
};
xmlhttp.open("GET", "json_demo_db.php?x=" + dbParam, true);
xmlhttp.send();
Example explained:

Define an object containing a table property and a limit property.
Convert the object into a JSON string.
Send a request to the PHP file, with the JSON string as a parameter.
Wait until the request returns with the result (as JSON)
Display the result received from the PHP file.

Take a look at the PHP file:
PHP file
<?php
header("Content-Type: application/json; charset=UTF-8");
$obj = json_decode($_GET["x"], false);

$conn = new mysqli("myServer", "myUser", "myPassword", "Northwind");
$stmt = $conn->prepare("SELECT name FROM ? LIMIT ?");
$stmt->bind_param("ss", $obj->table, $obj->limit);
$stmt->execute();
$result = $stmt->get_result();
$outp = $result->fetch_all(MYSQLI_ASSOC);

echo 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, and return the object as JSON using the json_encode() function.

Loop Through the Result

Convert the result received from the PHP file into a JavaScript object, or in this case, a JavaScript array:
Example

Use JSON.parse() to convert the JSON into a JavaScript object:
...
xmlhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
myObj = JSON.parse(this.responseText);
for (x in myObj) {
txt += myObj[x].name + "<br>";
}
document.getElementById("demo").innerHTML = txt;
}
};
...
PHP Method = POST

When sending data to the server, it is often best to use the HTTP POST method.

To send AJAX requests using the POST method, specify