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localstorage.js
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Sun, Jan 26, 20:13

localstorage.js
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/**
* A localStorage-only method which uses localstorage and its 'storage'-event
* This does not work inside of webworkers because they have no access to locastorage
* This is basically implemented to support IE9 or your grandmothers toaster.
* @link https://caniuse.com/#feat=namevalue-storage
* @link https://caniuse.com/#feat=indexeddb
*/
import { ObliviousSet } from 'oblivious-set';
import {
fillOptionsWithDefaults
} from '../options';
import {
sleep,
randomToken,
microSeconds as micro,
isNode
} from '../util';
export const microSeconds = micro;
const KEY_PREFIX = 'pubkey.broadcastChannel-';
export const type = 'localstorage';
/**
* copied from crosstab
* @link https://github.com/tejacques/crosstab/blob/master/src/crosstab.js#L32
*/
export function getLocalStorage() {
let localStorage;
if (typeof window === 'undefined') return null;
try {
localStorage = window.localStorage;
localStorage = window['ie8-eventlistener/storage'] || window.localStorage;
} catch (e) {
// New versions of Firefox throw a Security exception
// if cookies are disabled. See
// https://bugzilla.mozilla.org/show_bug.cgi?id=1028153
}
return localStorage;
}
export function storageKey(channelName) {
return KEY_PREFIX + channelName;
}
/**
* writes the new message to the storage
* and fires the storage-event so other readers can find it
*/
export function postMessage(channelState, messageJson) {
return new Promise(res => {
sleep().then(() => {
const key = storageKey(channelState.channelName);
const writeObj = {
token: randomToken(),
time: new Date().getTime(),
data: messageJson,
uuid: channelState.uuid
};
const value = JSON.stringify(writeObj);
getLocalStorage().setItem(key, value);
/**
* StorageEvent does not fire the 'storage' event
* in the window that changes the state of the local storage.
* So we fire it manually
*/
const ev = document.createEvent('Event');
ev.initEvent('storage', true, true);
ev.key = key;
ev.newValue = value;
window.dispatchEvent(ev);
res();
});
});
}
export function addStorageEventListener(channelName, fn) {
const key = storageKey(channelName);
const listener = ev => {
if (ev.key === key) {
fn(JSON.parse(ev.newValue));
}
};
window.addEventListener('storage', listener);
return listener;
}
export function removeStorageEventListener(listener) {
window.removeEventListener('storage', listener);
}
export function create(channelName, options) {
options = fillOptionsWithDefaults(options);
if (!canBeUsed()) {
throw new Error('BroadcastChannel: localstorage cannot be used');
}
const uuid = randomToken();
/**
* eMIs
* contains all messages that have been emitted before
* @type {ObliviousSet}
*/
const eMIs = new ObliviousSet(options.localstorage.removeTimeout);
const state = {
channelName,
uuid,
eMIs // emittedMessagesIds
};
state.listener = addStorageEventListener(
channelName,
(msgObj) => {
if (!state.messagesCallback) return; // no listener
if (msgObj.uuid === uuid) return; // own message
if (!msgObj.token || eMIs.has(msgObj.token)) return; // already emitted
if (msgObj.data.time && msgObj.data.time < state.messagesCallbackTime) return; // too old
eMIs.add(msgObj.token);
state.messagesCallback(msgObj.data);
}
);
return state;
}
export function close(channelState) {
removeStorageEventListener(channelState.listener);
}
export function onMessage(channelState, fn, time) {
channelState.messagesCallbackTime = time;
channelState.messagesCallback = fn;
}
export function canBeUsed() {
if (isNode) return false;
const ls = getLocalStorage();
if (!ls) return false;
try {
const key = '__broadcastchannel_check';
ls.setItem(key, 'works');
ls.removeItem(key);
} catch (e) {
// Safari 10 in private mode will not allow write access to local
// storage and fail with a QuotaExceededError. See
// https://developer.mozilla.org/en-US/docs/Web/API/Web_Storage_API#Private_Browsing_Incognito_modes
return false;
}
return true;
}
export function averageResponseTime() {
const defaultTime = 120;
const userAgent = navigator.userAgent.toLowerCase();
if (userAgent.includes('safari') && !userAgent.includes('chrome')) {
// safari is much slower so this time is higher
return defaultTime * 2;
}
return defaultTime;
}
export default {
create,
close,
onMessage,
postMessage,
canBeUsed,
type,
averageResponseTime,
microSeconds
};

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