get data attribute - getAttribute('data-part-id')

In this example we have a list of links that have a data-part-id="" attribute. When clicked, the attribute value is obtained and printed to the screen.

var getPartId = function(event){
	event.preventDefault();
	var partId = this.getAttribute('data-part-id');
	document.getElementById('partIdDisplay').children[0].innerHTML = partId;
};

var partsList = document.getElementById('partsList');

for(var i = 0; i < partsList.children.length; i++){
	partsList.children[i].children[0].addEventListener('click',getPartId,false);
};

fetch json data from php script, return values into html

var user_id_text = document.getElementById('user_id_text');
var fname = document.getElementById('fname');
var lname = document.getElementById('lname');
var phone = document.getElementById('phone');
var email = document.getElementById('email');

function getUserData(user_id){
	fetch('echo.json.php',{
		method: 'POST',
		headers: {'Content-Type':'application/json'},
		body: JSON.stringify({user_id:user_id,misc_value:'misc value'})
		//headers: {'Content-Type':'application/x-www-form-urlencoded'},
		//body: 'user_id=' + user_id
	})
	.then(function(res){
		return res.json()
		//return res.text()
	})
	.then(function(data){
	   user_id_text.innerHTML = data.user_id;
	   fname.innerHTML = data.fname;
	   lname.innerHTML = data.lname;
	   phone.innerHTML = data.phone;
	   email.innerHTML = data.email;
	})
}

document.getElementById('usersList').addEventListener('change',function(){
	var user_id = this.value;
	if(user_id != ''){
		getUserData(user_id);
	}
});

header('Content-Type: application/json; charset=UTF-8');
$data = json_decode(file_get_contents('php://input'), true);
$user_id = $data['user_id'];
if($user_id == 1){
	$data = array(
		'user_id' => $user_id,
		'fname' => 'Andrew',
		'lname' => 'Mabry',
		'phone' => '512-777-1085',
		'email' => 'andrew@elp7.com'
	);
}
if($user_id == 2){
	$data = array(
		'user_id' => $user_id,
		'fname' => 'Charles',
		'lname' => 'Mabry',
		'phone' => '512-786-7729',
		'email' => 'charles@elp7.com'
	);	
}
if($user_id == 3){
	$data = array(
		'user_id' => $user_id,
		'fname' => 'Juliana',
		'lname' => 'Azar',
		'phone' => '512-459-2222',
		'email' => 'juliana.azar@gmail.com'
	);		
}
print json_encode($data);