Summary of several APIs or tips in HTML5 that cannot be missed

<section contextmenu="mymenu">
<!--
For the purpose of cleanliness,
I'll put my menu inside the element that will use it
-->
<!-- add the menu -->
<menu type="context" id="mymenu">
<menuitem label="Refresh Post" onclick="window.location.reload();" icon="/images/refresh-icon.png"></menuitem>
<menu label="Share on..." icon="/images/share_icon.gif">
<menuitem label="Twitter" icon="/images/twitter_icon.gif" onclick="goTo('//twitter.com/intent/tweet?text=' + document.title + ': ' + window.location.href);"></menuitem>
<menuitem label="Facebook" icon="/images/facebook_icon16x16.gif" onclick="goTo('//facebook.com/sharer/sharer.php?u=' + window.location.href);"></menuitem>
</menu>
</menu>
</section>

<div id="myDiv" data-name="myDiv" data-id="myId" data-my-custom-key="This is the value"></div>

// Get the element
var element = document.getElementById("myDiv");
// Get id
var id = element.dataset.id;
// Get data-my-custom-key"
var customKey = element.dataset.myCustomKey;
// Set the new value
element.dataset.myCustomKey = "Some other value";

// From window or frame on domain 1, send a message to the iframe which hosts another domain
var iframeWindow = document.getElementById("iframe").contentWindow;
iframeWindow.postMessage("Hello from the first window!");
// From inside the iframe on different host, receive message
window.addEventListener("message", function(event) {
if (event.origin == "http://davidwalsh.name") {
// Log out the message
console.log(event.data);
// Send a message back
event.source.postMessage("Hello back!");
}
]);

<input autofocus="autofocus" />
<button autofocus="autofocus">Hi!</button>
<textarea autofocus="autofocus"></textarea>