@richlewis42/callable
v0.2.1
Published
Callable instances for JS
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@richlewis42/callable
Callable instances for JS, in under 10 lines of ES6!
Motivation
Anything class be a function in Python simply by implementing a __call__
method.
For example,
class ImaFunc(object):
def __init__(self, a):
super()
self.a = a
@property
def b(self):
return self.a + 10
def __call__(self, c):
return [self.a, self.b, c]
f = ImaFunc(10)
f(30) # [10, 20, 30]
This can be really useful: the callable method has access to the member attributes and properties, so we can change how the function behaves post instatiation:
f.a = 40
f(60) # [40, 50, 60]
Additionally, the instance works with the class hierarchy nicely:
isinstance(f, ImaFunc) # True
isinstance(f, object) # True
callable(f) # True
However, in JavaScript, this is not so straightforward... until now!!
Install
For node
:
npm install @richlewis/callable
For the browser, you can include a script tag to pull the library from unpkg:
<script
type="text/javascript"
src="https://unpkg.com/@richlewis/callable"
></script>
Usage
Inherit from the default export of this library, Callable
:
class ImaFunc extends Callable {
constructor(a) {
super()
this.a = a
}
get b() {
return this.a + 10
}
__call__(c) {
return [this.a, this.b, c]
}
}
const f = new ImaFunc(10)
f(30) // [10, 20, 30]
f instanceof ImaFunc // true
f instanceof Callable // true
f instanceof Object // true
f instanceof Function // true
Now you can do some func-y tricks:
class SubFunc extends ImaFunc {
constructor(a, d) {
super(a)
this.d = d
}
get e() {
return this.d + 10
}
__call__(c, f) {
return [...super.__call__(c), this.d, this.e, f]
}
}
new SubFunc(10, 40)(30, 60) // [10, 20, 30, 40, 50, 60]
How does it work?
Callable hijacks the constructor, returning a function
that executes the __call__
function bound to itself.
This function gets the prototype and member properties from the this
object, and thus the inheritance chain is repaired!
Prior Art
Other libraries that present similar functionality: