sistematico/callback.php

## callback.php
<?php

$array = array(
    array('texto'=>'Olá ' . $_POST['nome'] . '!'),
    array('texto'=>'Bem-vindo(a) ' . $_POST['nome']),
    array('texto'=>'Tudo bem ' . $_POST['nome'])
);

echo json_encode($array);

## get.php
<?php

echo "Lorem, ipsum dolor sit amet consectetur adipisicing elit. Nostrum repellendus doloremque consectetur sed esse autem quos dignissimos recusandae velit eum qui voluptatibus vitae obcaecati id repellat aspernatur, eaque ipsa aliquid?";

## index.html
<!DOCTYPE html>
<html lang="pt-br">
  <head>
    <meta charset="utf-8" />
    <meta http-equiv="x-ua-compatible" content="ie=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <title>XMLHttpRequest</title>
  </head>
  <body>
    Código em: <a href="https://gist.github.com/sistematico/c1bdf247c69edd60206b48fa9bc4cf11">https://gist.github.com/sistematico/c1bdf247c69edd60206b48fa9bc4cf11</a>
    <br /><br />
    <button id="getBtn">XHR Get</button> <div id="resultadoGet"></div><br /><br />
    <button id="postBtn">XHR Post</button> <div id="resultadoPost"></div><br /><br />
    <button id="jsonBtn">XHR Json</button> <div id="resultadoJson"></div><br /><br />
    <button id="callbackBtn">XHR Callback</button> <div id="resultadoCallback"></div><br /><br />

    <script src="xhr.js"></script>
    <script src="xhrpost.js"></script>
    <script src="xhrjson.js"></script>
    <script src="xhrcallback.js"></script>
  </body>
</html>

## json.php
<?php

$array = array(
    array('texto'=>'Algum texto'),
    array('texto'=>'Algum outro texto'),
    array('texto'=>'E mais algum texto')
);

echo json_encode($array);

## post.php
<?php

echo $_POST['lorem'];

## xhr.js
const getBtn = document.getElementById("getBtn");
const resultadoGet = document.getElementById("resultadoGet");

let xhr = (url,div) => {
    xmlhttp = new XMLHttpRequest();
    xmlhttp.onreadystatechange = function () {
        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            div.innerHTML = xmlhttp.responseText;
        }
    }
    xmlhttp.open("GET", url, true);
    xmlhttp.send();
};

getBtn.onclick = function(){
    xhr('get.php', resultadoGet);
};

## xhrcallback.js
const callbackBtn = document.getElementById("callbackBtn");
const resultadoCallback = document.getElementById("resultadoCallback");

let xhrCallback = (url, method, cb, params = null) => {
    xmlhttp = new XMLHttpRequest();
    xmlhttp.open(method, url, true);

    if (method === 'post') {
        xmlhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
    }

    xmlhttp.onreadystatechange = function () {
        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            cb(xmlhttp.responseText);
        }
    }
    xmlhttp.send(params);
};

let callback = (resposta) => {
    let saida = '';
    data = JSON.parse(resposta);

    data.forEach((el, i) => {
        saida += data[i].texto + '<br />';
    });

    resultadoCallback.innerHTML = saida;
};

callbackBtn.onclick = function(){
    xhrCallback('callback.php', 'post', callback, 'nome=Joao&sobrenome=Silva');
};

## xhrjson.js
const jsonBtn = document.getElementById("jsonBtn");
const resultadoJson = document.getElementById("resultadoJson");

let xhrJson = (url, div) => {
    xmlhttp = new XMLHttpRequest();
    xmlhttp.onreadystatechange = function () {
        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            let objetos = JSON.parse(xmlhttp.responseText);
            let saida = '';
            let i;
            for(i = 0; i < objetos.length; i++) {
                //saida += '<a href="' + objetos[i].id + '">' + objetos[i].artista + '</a><br>';
                saida += objetos[i].texto + '</a><br>';
            }
            div.innerHTML = saida;
        }
    }
    xmlhttp.open("GET", url, true);
    xmlhttp.send();
};

jsonBtn.onclick = function(){
    xhrJson('json.php', resultadoJson);
};

## xhrpost.js
const postBtn = document.getElementById("postBtn");
const resultadoPost = document.getElementById("resultadoPost");

let xhrPost = (url,params,div) => {
    xmlhttp = new XMLHttpRequest();
    xmlhttp.open('POST', url, true);
    xmlhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
    xmlhttp.onreadystatechange = function () {
        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            div.innerHTML = xmlhttp.responseText;
        }
    }
    xmlhttp.send(params);
};

postBtn.onclick = function(){
    xhrPost('post.php', 'lorem=ipsum&ipsum=lorem', resultadoPost);
};
	<?php

	$array = array(
	array('texto'=>'Olá ' . $_POST['nome'] . '!'),
	array('texto'=>'Bem-vindo(a) ' . $_POST['nome']),
	array('texto'=>'Tudo bem ' . $_POST['nome'])
	);

	echo json_encode($array);
	<?php

	echo "Lorem, ipsum dolor sit amet consectetur adipisicing elit. Nostrum repellendus doloremque consectetur sed esse autem quos dignissimos recusandae velit eum qui voluptatibus vitae obcaecati id repellat aspernatur, eaque ipsa aliquid?";
	<!DOCTYPE html>
	<html lang="pt-br">
	<head>
	<meta charset="utf-8" />
	<meta http-equiv="x-ua-compatible" content="ie=edge" />
	<meta name="viewport" content="width=device-width, initial-scale=1" />
	<title>XMLHttpRequest</title>
	</head>
	<body>
	Código em: <a href="https://gist.github.com/sistematico/c1bdf247c69edd60206b48fa9bc4cf11">https://gist.github.com/sistematico/c1bdf247c69edd60206b48fa9bc4cf11</a>
	<br /><br />
	<button id="getBtn">XHR Get</button> <div id="resultadoGet"></div><br /><br />
	<button id="postBtn">XHR Post</button> <div id="resultadoPost"></div><br /><br />
	<button id="jsonBtn">XHR Json</button> <div id="resultadoJson"></div><br /><br />
	<button id="callbackBtn">XHR Callback</button> <div id="resultadoCallback"></div><br /><br />

	<script src="xhr.js"></script>
	<script src="xhrpost.js"></script>
	<script src="xhrjson.js"></script>
	<script src="xhrcallback.js"></script>
	</body>
	</html>
	<?php

	$array = array(
	array('texto'=>'Algum texto'),
	array('texto'=>'Algum outro texto'),
	array('texto'=>'E mais algum texto')
	);

	echo json_encode($array);
	const getBtn = document.getElementById("getBtn");
	const resultadoGet = document.getElementById("resultadoGet");

	let xhr = (url,div) => {
	xmlhttp = new XMLHttpRequest();
	xmlhttp.onreadystatechange = function () {
	if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
	div.innerHTML = xmlhttp.responseText;
	}
	}
	xmlhttp.open("GET", url, true);
	xmlhttp.send();
	};

	getBtn.onclick = function(){
	xhr('get.php', resultadoGet);
	};
	const callbackBtn = document.getElementById("callbackBtn");
	const resultadoCallback = document.getElementById("resultadoCallback");

	let xhrCallback = (url, method, cb, params = null) => {
	xmlhttp = new XMLHttpRequest();
	xmlhttp.open(method, url, true);

	if (method === 'post') {
	xmlhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
	}

	xmlhttp.onreadystatechange = function () {
	if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
	cb(xmlhttp.responseText);
	}
	}
	xmlhttp.send(params);
	};

	let callback = (resposta) => {
	let saida = '';
	data = JSON.parse(resposta);

	data.forEach((el, i) => {
	saida += data[i].texto + '<br />';
	});

	resultadoCallback.innerHTML = saida;
	};

	callbackBtn.onclick = function(){
	xhrCallback('callback.php', 'post', callback, 'nome=Joao&sobrenome=Silva');
	};
	const jsonBtn = document.getElementById("jsonBtn");
	const resultadoJson = document.getElementById("resultadoJson");

	let xhrJson = (url, div) => {
	xmlhttp = new XMLHttpRequest();
	xmlhttp.onreadystatechange = function () {
	if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
	let objetos = JSON.parse(xmlhttp.responseText);
	let saida = '';
	let i;
	for(i = 0; i < objetos.length; i++) {
	//saida += '<a href="' + objetos[i].id + '">' + objetos[i].artista + '</a><br>';
	saida += objetos[i].texto + '</a><br>';
	}
	div.innerHTML = saida;
	}
	}
	xmlhttp.open("GET", url, true);
	xmlhttp.send();
	};

	jsonBtn.onclick = function(){
	xhrJson('json.php', resultadoJson);
	};
	const postBtn = document.getElementById("postBtn");
	const resultadoPost = document.getElementById("resultadoPost");

	let xhrPost = (url,params,div) => {
	xmlhttp = new XMLHttpRequest();
	xmlhttp.open('POST', url, true);
	xmlhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
	xmlhttp.onreadystatechange = function () {
	if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
	div.innerHTML = xmlhttp.responseText;
	}
	}
	xmlhttp.send(params);
	};

	postBtn.onclick = function(){
	xhrPost('post.php', 'lorem=ipsum&ipsum=lorem', resultadoPost);
	};