Posted 10 months ago. Visible to the public.

JavaScript: Hash/Object with default value

You can easily have a JavaScript hash/object that returns a default value for unset keys/properties – as long as you need to support only recent browsers.

The key are JavaScript proxies from ECMAScript 6 that allow implementing a custom getter method. They work like this:

var hash = new Proxy({}, { get: function(object, property) { return object.hasOwnProperty(property) ? object[property] : 'hello'; } });

When you set a key, you can read its value just like always.

hash['foo'] = 23 hash['foo'] // => 23

But instead of returning undefined for unset keys, our get proxy now returns our default value.

hash['bar'] // => 'hello'

This is supported in Chrome 49+, Firefox 18+, Safari 10+, and Edge 13+.

Once an application no longer requires constant development, it needs periodic maintenance for stable and secure operation. makandra offers monthly maintenance contracts that let you focus on your business while we make sure the lights stay on.

Author of this card:

Arne Hartherz
Last edit:
10 months ago
by Arne Hartherz
About this deck:
We are makandra and do test-driven, agile Ruby on Rails software development.
License for source code
Posted by Arne Hartherz to makandropedia