getExtensions

getExtensions is a method, which takes one parameter, cacheInstance, and returns an object with new method. Passed cacheInstance can but not necessarily must be used.

Example without the use of cacheInstance:

getExtensions: () => {
    return {
        logTimestamp: (logger) => {
            const date = new Date();

            logger.log(date.toUTCString());
        }
    }
}

Once cache instance has a plugin registered with this method, it can be used like so:

// providing that this plugin was registered
cache.logTimestamp(console); // this will run console.log with UTC string date

Example with the use of passed cacheInstance:

getExtensions: (cacheInstance) => {
    return {
        getItems: (keys) => {
            return keys.forEach(cacheInstance.getItem);
        }
    }
}

Above method, getItems, when passed an array of keys to it, will return an array of items (if found). Usage will look like this:

// providing that this plugin was registered
cache.getItems([ 'foo', 'bar', 'keyForItemThatDoesNotExist' ]); // [ itemFoo, itemBar, undefined ]

What about lifecycle of such created methods?

Well, you need to add them. For that you will need getPreData and getPostData methods available in stash-it.

Here's how it would look like for getItems method we created in previous example:

import { getPreData, getPostData } from 'stash-it';

// excerpt of given plugin, hence only getExtensions here
getExtensions: (cacheInstance) => {
    return {
        getItems: (keys) => {
            const preData = getPreData('getItems', { keys, cacheInstance });
            const items = preData.keys.map(cacheInstance.getItem);
            const postData = getPostData('getItems', { keys: preData.keys, items, cacheInstance: preData.cacheInstance });

            return postData.items; 
        }
    }
}

And that's it. Your new method is ready for events preGetItems and postGetItems. If you would be a creator of such a plugin, your responsibility is to provide detailed information how lifecycle of such a method looks like:

• what event names are here (by convention it's the same as created method's name, plus prefixes);
• what properties are passed in 2nd argument to getPreData and getPostData;
• what should be returned by each method (getPreData and getPostData);
• what is returned by newly created method - here getItems.

Now, this method should have some data validation etc. but this is not the case of this example.

For more information how a complete plugin should look like, head straight to writing plugins.