esprehn/gist:718242dbcae337d8c67d

## gistfile1.txt
<!DOCTYPE html>

<body>

<template id="template">
    <style>
        :host { color: red; display: block; }
    </style>
    <div>Example</div>
</template>

<script>
var template = document.getElementById("template");

function createdCallback() {
/*
NEVER INLINE.

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
proident, sunt in culpa qui officia deserunt mollit anim id est laborum. Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
*/

    this.createShadowRoot().appendChild(document.importNode(template, true));
}

var proto = Object.create(HTMLElement.prototype);
proto.createdCallback = createdCallback;
var XRealElement = document.registerElement("x-real-element", { prototype: proto });

var kElementCount = 10000;

function noCustomElement() {
    var text = "";
    for (var i = 0; i < kElementCount; ++i) {
        text += "<x-fake-element></x-fake-element>";
    }
    var t = performance.now();
    var widget = document.createElement("div");
    widget.innerHTML = text;
    for (var child = widget.firstElementChild; child; child = child.nextElementSibling) {
        createdCallback.call(child);
    }
    document.body.appendChild(widget);
    console.log("noCustomElement", performance.now() - t);
}

function realCustomElement() {
    var t = performance.now();
    var widget = document.createElement("div");
    for (var i = 0; i < kElementCount; ++i) {
        var element = document.createElement("x-real-element");
        widget.appendChild(element);
    }
    document.body.appendChild(widget);
    console.log("realCustomElement", performance.now() - t);
}

function fakeCustomElement() {
    var t = performance.now();
    var widget = document.createElement("div");
    for (var i = 0; i < kElementCount; ++i) {
        var element = document.createElement("x-fake-element");
        createdCallback.call(element);
        widget.appendChild(element);
    }
    document.body.appendChild(widget);
    console.log("fakeCustomElement", performance.now() - t);
}

function fakeCustomElementWithProto() {
    var t = performance.now();
    var widget = document.createElement("div");
    for (var i = 0; i < kElementCount; ++i) {
        var element = document.createElement("x-fake-element");
        element.__proto__ = XRealElement.prototype;
        createdCallback.call(element);
        widget.appendChild(element);
    }
    document.body.appendChild(widget);
    console.log("fakeCustomElementWithProto", performance.now() - t);
}

function fakeCustomElementMoreCrossing() {
    var t = performance.now();
    var widget = document.createElement("div");
    for (var i = 0; i < kElementCount; ++i) {
        var element = document.createElement("x-fake-element");
        createdCallback.call(element);
        var noop = element.shadowRoot.getElementById("test");
        widget.appendChild(element);
    }
    document.body.appendChild(widget);
    console.log("fakeCustomElementMoreCrossing", performance.now() - t);
}

noCustomElement();
fakeCustomElement();
realCustomElement();
fakeCustomElementWithProto();
fakeCustomElementMoreCrossing();
</script>
	<!DOCTYPE html>

	<body>

	<template id="template">
	<style>
	:host { color: red; display: block; }
	</style>
	<div>Example</div>
	</template>

	<script>
	var template = document.getElementById("template");

	function createdCallback() {
	/*
	NEVER INLINE.

	Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
	tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
	quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
	consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
	cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
	proident, sunt in culpa qui officia deserunt mollit anim id est laborum. Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
	tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
	quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
	consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
	cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
	proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
	*/

	this.createShadowRoot().appendChild(document.importNode(template, true));
	}

	var proto = Object.create(HTMLElement.prototype);
	proto.createdCallback = createdCallback;
	var XRealElement = document.registerElement("x-real-element", { prototype: proto });

	var kElementCount = 10000;

	function noCustomElement() {
	var text = "";
	for (var i = 0; i < kElementCount; ++i) {
	text += "<x-fake-element></x-fake-element>";
	}
	var t = performance.now();
	var widget = document.createElement("div");
	widget.innerHTML = text;
	for (var child = widget.firstElementChild; child; child = child.nextElementSibling) {
	createdCallback.call(child);
	}
	document.body.appendChild(widget);
	console.log("noCustomElement", performance.now() - t);
	}

	function realCustomElement() {
	var t = performance.now();
	var widget = document.createElement("div");
	for (var i = 0; i < kElementCount; ++i) {
	var element = document.createElement("x-real-element");
	widget.appendChild(element);
	}
	document.body.appendChild(widget);
	console.log("realCustomElement", performance.now() - t);
	}

	function fakeCustomElement() {
	var t = performance.now();
	var widget = document.createElement("div");
	for (var i = 0; i < kElementCount; ++i) {
	var element = document.createElement("x-fake-element");
	createdCallback.call(element);
	widget.appendChild(element);
	}
	document.body.appendChild(widget);
	console.log("fakeCustomElement", performance.now() - t);
	}

	function fakeCustomElementWithProto() {
	var t = performance.now();
	var widget = document.createElement("div");
	for (var i = 0; i < kElementCount; ++i) {
	var element = document.createElement("x-fake-element");
	element.__proto__ = XRealElement.prototype;
	createdCallback.call(element);
	widget.appendChild(element);
	}
	document.body.appendChild(widget);
	console.log("fakeCustomElementWithProto", performance.now() - t);
	}

	function fakeCustomElementMoreCrossing() {
	var t = performance.now();
	var widget = document.createElement("div");
	for (var i = 0; i < kElementCount; ++i) {
	var element = document.createElement("x-fake-element");
	createdCallback.call(element);
	var noop = element.shadowRoot.getElementById("test");
	widget.appendChild(element);
	}
	document.body.appendChild(widget);
	console.log("fakeCustomElementMoreCrossing", performance.now() - t);
	}

	noCustomElement();
	fakeCustomElement();
	realCustomElement();
	fakeCustomElementWithProto();
	fakeCustomElementMoreCrossing();
	</script>