popup.js

const $ = (v) => document.querySelector(v);
const $$ = (v) => document.querySelectorAll(v);
let changeColorBtn = $$(".changeColor");

chrome.storage.sync.get("bgcolor", function (data) {
	const { bgcolor } = data;
	for (let i = 0; i < bgcolor.length; i++) {
		changeColorBtn[i].style.backgroundColor = bgcolor[i];
	}
	
	const randomIdx = randomNum(bgcolor.length);
	const code = `document.body.style.backgroundColor = "${bgcolor[randomIdx]}";
				document.querySelector("#contents").style.color = "#eee";`;
	chrome.tabs.query({ active: true, currentWindow: true }, function (tabs) {
		chrome.tabs.executeScript(tabs[0].id, {
			code: `${code}`,
		});
	});
});

for (let i = 0; i < changeColorBtn.length; i++) {
	changeColorBtn[i].addEventListener("click", function (e) {
		chrome.storage.sync.get("bgcolor", function (data) {
			const { bgcolor } = data;
			chrome.tabs.query({ active: true, currentWindow: true }, function (tabs) {
				chrome.tabs.executeScript(tabs[0].id, {
					code: `document.body.style.backgroundColor = "${bgcolor[i]}";`,
				});
			});
		});
	});
}

function randomNum(length) {
	return Math.floor(Math.random() * length)
}