Late binding of overridable object properties.
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README.md

bind-late npm version

Late binding of overridable object properties.

Description

Define an overridable object where special "late binded" functions will be treated as lazy memoized properties.

All the functions in the object structure that are anonymous and take a single _ argument, are considered to be "late bindings". When the property is accessed the first time, they are called with the final overridden object as _ parameter, and their return value is affected to the property.

Nesting

You can nest late binded objects. Late binded objects are not plain objects and will not be recursively extended during an override, so you need to extend them explicitely (this is often what you want, since override would otherwise just copy your properties and not rebuild the inner late binded object according to what you changed).

Example

const bindLate = require('bind-late')

const a = bindLate({
  a: 8,
  b: {
    c: 2,
    d: _ => _.a + _.b.c,
  },
  e: _ => _.b.d * 2,
})

a.b.d === 10 // 8 + 2
a.e === 20 // 10 * 2

const b = a.override({ a: 6 })

b.b.d === 8 // 6 + 2
b.e === 16 // 8 * 2

const c = b.override({
  b: { c: 6 },
  e: _ => _.b.d - 2,
})

c.b.d === 12 // 6 + 6
c.e === 10 // 12 - 2

You can also watch the antisocial-auth source code for a more concrete example, where everything is overridable thanks to bind-late.

Demo

See the demo directory to see a functional example you can tweak and play with.