xet

xet( map, key, factory ) // => If map doesn't have key, set it to the return value of factory. Return value.

Usage no npm install needed!

<script type="module">
  import xet from 'https://cdn.skypack.dev/xet';
</script>

README

Build Status

xet ([ʃɛt]) retrieves a map's value for a given key, setting it with a provided factory if it isn't present.

xet( map, key, factory )
// where
const factory = (key, value) => value

This is useful when writing in a point-free declarative dialect - virtual DOM view templates for example - and want to write functions that can conditionally run setup in the form of the factory.