createTTL

Function for creating custom TTL handlers in JavaScript. Set expiration for keys and get notified when a key is expired.

Usage

Include ttl.js in your web page (or load it with AMD).

<script src="ttl.js"></script>

For a locasStorage based example, check out localstorage-ttl.js and localstorage-ttl.html which bundles this TTL API into a localStorage backed solution.

Create TTL handler

Create a new TTL handler interface with createTTL

var ttl = createTTL([seed]);
ttl.start();

Where

• seed is the last known state of a previous TTL handler (the state is reveived from the #onupdate notification)

start() must be called after the ttl object is set up. Do not call it before you set the onupdate and onexpire handlers, otherwise you might get a race condition where an expiration is detected and emitted before you have set the handlers.

Example

var lastState = JSON.parse(localStorage.getItem('ttlInfo'));
var ttl = createTTL(lastState);
ttl.start();

Resetting state

If you need to clear the current state and use updated one, use reset

ttl.reset(state);

Where

• state is the last known state of a previous TTL handler

Example

var ttl = createTTL();
ttl.start();
var state = JSON.parse(localStorage.getItem('ttlInfo'));
ttl.reset(state); // drop existing state and replace it with loaded state

Set TTL for a key

Set the TTL value for a key with set

ttl.set(key, expire);

Where

• key is the name of the key
• expire is the TTL in milliseconds. If this value is 0 or negative, any existing TTL is cleared

Example

var ttl = createTTL();
ttl.start();
ttl.set('mykey', 1000); // expire in 1 second

Get remaining TTL for a key

Get the TTL value for a key with get

var remaining = ttl.get(key);

Where

• key is the name of the key

Example

var ttl = createTTL();
ttl.start();
var remaining = ttl.get('mykey');

Get notified about expired key

Get notifications with the onexpire method

ttl.onexpire = function(key){};

Where

• key is the expired key name

Example

var ttl = createTTL();
ttlhandler.onexpire = function(key){
    // remove expired key from localStorage
    localStorage.removeItem(key);
};
ttl.start();

Get notified about changes in TTL metadata

To be able to continue with TTLs when page is reloaded, you should store the TTL state if anything changes.

ttl.onupdate = function(state){};

Where

• state is the updated state of the TTL handler

example

var ttl = createTTL();
ttlhandler.onexpire = function(state){
    // Store serialized state data to localStorage
    localStorage.setItem('ttlInfo', JSON.stringify(state));
};
ttl.start();

License

MIT