When using persistent enmaps, it's very important to understand that it takes time to load the data from the database. Attempting to use the enmap before it's fully loaded can lead to errors, so we need to make sure it's ready before using it.

Using defer

To make sure that all your data is loaded before you start working, Enmap provides a handy property called defer, which is a promise that is resolved once SQLite is ready and all the data has been loaded into memory. There are a few ways to use defer, since it's a promise.

const Enmap = require('enmap');
const myEnmap = new Enmap({ name: 'test' });
​
// Using the standard .then() promise method: 
​
myEnmap.defer.then( () => {
  console.log(myEnmap.size + " keys loaded");
  myEnmap.set("blah", "foo"); // works
  myEnmap.get("thing"); // also works
});
​
// Using async/await as an immediate function: 
(async function() {
  await myEnmap.defer;
  console.log(myEnmap.size + " keys loaded");
  // Ready to use!
}());
​
// In an EventEmitter context:
myEmitter.on("eventName", async (arg) => {
  await myEnmap.defer;
  console.log(myEnmap.size + " keys loaded");
});

For more information on async/await and promises, see My JavaScript Guide.

Checking for Ready

Enmap also provides a isReady option that tells you if the database is loaded. You can use that however you want, though the preferred method is using defer.

if(myEnmap.isReady) { 
  // database is ready
} else {
  // database isn't loaded yet
}