e111077/background.html

## background.html
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title></title>
</head>
<body>
</body>
</html>

## contentScript.bundle.js
class A extends HTMLElement {
    foo () {
        console.log('FOO');
        // do stuff
    }
    constructor() {
      super();
        console.log(this.foo);
        this.foo(); // this.foo is undefined
    }
}


customElements.define('a-a', A);
const a = document.createElement('a-a');
document.body.appendChild(a);

## manifest.json
{
	"name": "Extension test",
	"background": {
		"page": "background.html"
	},
	"content_scripts": [
		{
			"matches": [
				"http://*/*",
				"https://*/*",
				"ftp://*/*",
				"file://*/*"
			],
			"js": [
				"contentScript.bundle.js"
			]
		}
	],
	"icons": {
	},
	"manifest_version": 2,
	"version": "1.0"
}
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<title></title>
	</head>
	<body>
	</body>
	</html>
	class A extends HTMLElement {
	foo () {
	console.log('FOO');
	// do stuff
	}
	constructor() {
	super();
	console.log(this.foo);
	this.foo(); // this.foo is undefined
	}
	}


	customElements.define('a-a', A);
	const a = document.createElement('a-a');
	document.body.appendChild(a);
	{
	"name": "Extension test",
	"background": {
	"page": "background.html"
	},
	"content_scripts": [
	{
	"matches": [
	"http:///",
	"https:///",
	"ftp:///",
	"file:///"
	],
	"js": [
	"contentScript.bundle.js"
	]
	}
	],
	"icons": {
	},
	"manifest_version": 2,
	"version": "1.0"
	}