@browndragon/switch-type
v0.0.13
Published
An improved `typeof` handler.
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@browndragon/switch-type
Install & use with $ npm i @browndragon/switch-type
and then
import switchType from '@browndragon/switch-type';
switchType(
undefined,
{default(x, ...params) {console.log(`Default ${x} & params ${params}!`);}},
'someParam1', 'someParam2'
);
// Prints 'Default undefined & params someParam1,someParam2!'
Why switchType
?
I got very fed up with the mess that is javascript type introspection, so I wrote my own.
switchType(unknownObject, handler)
will do type analysis on the unknown object and then invoke the correctly named method on handler with the object.
The methods it will call are (roughly in order, omit irrelevants):
undefined
(will also trynull
)null
(will also tryundefined
)boolean
(avalue
)bigint
(avalue
)number
(avalue
)string
(avalue
and aniterable
)function
(avalue
)
Then we start considering (non-null) objects;
array
(aniterable
): Anything that isArray.isArray
.map
(anassociative
and aniterable
) -- usesinstanceof Map
(as do the other specialized types).set
(aniterable
)iterable
: Anything with aSymbol.iterator
on it (including collections & arrays & strings).regExp
: Aninstanceof RegExp
.literal
: an object whose prototype is literallyObject
(as created byObject.create
and the{}
syntax). Alsoassociative
.associative
: An object which@browndragon/obj
can get/set fields on. A Map or an object literal.
Finally, objects will try to call:
object
: Any non-null
jstypeof(x)=='object'
.
Finally-finally, anything will try to call:
default
: Anything that wasn't otherwise matched.
switchType
returns the result of the called method or else undefined
.
What about other "root types"?
To make this work, I've invented several new root types which "feel like" javascript basic types. To me.
- The
values
are mostly unobjectionable. - Everyone agrees the
undefined
/null
/class Object
situation is messy; this is just a semi-opinionated, semi-flexible way to cut through that. I don't considerundefined
ornull
to bevalues
in this library. Object
is the root of the object hierarchy, but is also used directly as a container.- As a container type, it's called a
literal
. - As the root of the object hierarchy, it's customized into a few builtin es6 types (Map, Set, Array, RegExp). You can add more with
withHandler
(which returns a new instance with the additional handlers) oraddHandler
(which modifies the handler in-place, possibly including the globally imported one!).
- As a container type, it's called a