Ushio-cn-old/yimian/iot/mqtt/smartfarm/node_modules/memdown

MemDOWN

A drop-in replacement for LevelDOWN that works in-memory. Can be used as a backend for LevelUP rather than an actual LevelDB store.

Example

As of version 0.7, LevelUP allows you to pass a 'db' option when you create a new instance. This will override the default LevelDOWN store with a LevelDOWN API compatible object. MemDOWN conforms exactly to the LevelDOWN API but only performs operations in memory, so your data is discarded when the process ends or you release a reference to the database.

var levelup = require('levelup')
  // note that if multiple instances point to the same location,
  // the db will be shared, but only per process
  , db = levelup('/some/location', { db: require('memdown') })

db.put('name', 'Clint Eastwood')
db.put('dob', 'May 31, 1930')
db.put('occupation', 'Badass')

db.readStream()
  .on('data', console.log)
  .on('close', function () { console.log('Go ahead, make my day!') })

Note in this example we're not even bothering to use callbacks on our .put() methods even though they are async. We know that MemDOWN operates immediately so the data will go straight into the store.

Running our example gives:

{ key: 'dob', value: 'May 31, 1930' }
{ key: 'name', value: 'Clint Eastwood' }
{ key: 'occupation', value: 'Badass' }
Go ahead, make my day!

Global Store

Even though it's in memory, the location parameter does do something. MemDOWN has a global cache, which it uses to save databases by the path string.

So for instance if you create these two MemDOWNs:

var db1 = levelup('foo', {db: require('memdown')});
var db2 = levelup('foo', {db: require('memdown')});

...they will actually share the same data, because the 'foo' string is the same.

You may clear this global store via the MemDOWN.clearGlobalStore() function:

require('memdown').clearGlobalStore();

By default, it doesn't delete the store but replaces it with a new one, so the open instance of MemDOWN will not be affected.

clearGlobalStore takes a single parameter, which if truthy clears the store strictly by deleting each individual key:

require('memdown').clearGlobalStore(true); // delete each individual key

If you are using MemDOWN somewhere else while simultaneously clearing the global store in this way, then it may throw an error or cause unexpected results.

Browser support

See .zuul.yml for the full list of browsers that are tested in CI.

But essentially, this module requires a valid ES5-capable browser, so if you're using one that's not ES5-capable (e.g. PhantomJS, Android < 4.4, IE < 10), then you will need the es5-shim.

Testing

npm install

Then:

npm test

Or to test in the browser using Saucelabs:

npm run test-browser

Or to test locally in your browser of choice:

npm run test-browser-local

To run the linter:

npm run lint

To check code coverage:

npm run coverage

Licence

MemDOWN is Copyright (c) 2013-2015 Rod Vagg @rvagg and licensed under the MIT licence. All rights not explicitly granted in the MIT license are reserved. See the included LICENSE file for more details.