WebExtension/background.js

let backgroundPage = browser.extension.getBackgroundPage();
let data;
let i=0;

data = readUrl()
.then(function(data){
		browser.browserAction.onClicked.addListener(function(event1){
				browser.tabs.create({"url": "home.html"},function(tab){
						browser.runtime.onMessage.addListener(function(request,sender,sendResponse){
								handleMessages(request,sender,sendResponse,tab,data);
						});
				});
		});
});

function handleMessages(message,sender,sendResponse,tab,data){
		if(message === "Button_clicked")
				{
				browser.tabs.executeScript(tab.id,{				
						file:"spawn.js"
				});
				console.log(tab);
				console.log(data);
				}
				else if(message === "Content_Loaded")
				{
						console.log("Background: Received Content_Loaded");
					//	nextUrl(data,tab,i);
						if(i===0)
						{
								browser.tabs.sendMessage(tab.id,"Init");
						}
						else
						{
								browser.tabs.sendMessage(tab.id,data.subscriptions[i].url);
						}
						console.log(i);
				}
				else if(message === "finished")
				{
						i++;
						console.log("background: received next from spawn.js");
						browser.tabs.update(tab.id,{url : data.subscriptions[i].url});
						browser.tabs.executeScript(tab.id,{				
								file:"spawn.js"
						});

						browser.tabs.sendMessage(tab.id,data.subscriptions[i].url);
				}
}

function readFile()
{
		const fileField = document.querySelector('input[type="file"]');
		fileField.addEventListener("change",() =>
				{
						console.log(fileField.files[0]);
				});
		var reader = new FileReader();




function readUrl()
{		
		let data;
		return  new Promise(resolve => {
		const filePath = "newpipe_subscriptions_202403101004.json";
		var localURL = browser.extension.getURL(filePath);
		fetch(localURL).then((res) => {
								if(!res.ok){
										throw new Error
											(`res error`);
								}
								return res.json();
						})
						.then((data) => {
								for(let i=0;i<i;i++) //i in data.subscriptions)
								{
										let open=null;
										console.log(data.subscriptions[i].url);
										try{
											open = alert(data.subscriptions[i].url,"_blank");
										}
										catch(e) {InsertError(e.description);}
								}
								console.log(data);
								resolve(data);
						})
						.catch((error)=> console.error("couldnt fetch data",error));
		});
}