What is zwitch?
The zwitch npm package is a utility for handling polymorphic dispatch based on a property value. It allows you to define a default handler and specific handlers for different values of a given property. This can be particularly useful for tasks like routing, handling different types of data structures, or implementing pattern matching in your code.
What are zwitch's main functionalities?
Handling different types of messages
This feature demonstrates how zwitch can be used to handle different types of messages based on their 'type' property. It shows setting up handlers for specific types and handling invalid or unknown types.
{"const zwitch = require('zwitch');\nconst handle = zwitch('type');\n\nhandle.invalid = (value) => { console.error('Invalid type:', value); };\nhandle.unknown = (value) => { console.error('Unknown type:', value); };\nhandle.handlers.string = (value) => { console.log('String:', value); };\nhandle.handlers.number = (value) => { console.log('Number:', value); };\n\nhandle({type: 'string', value: 'Hello, world!'});\nhandle({type: 'number', value: 42});\nhandle({type: 'boolean', value: true});"}
Default and specific handling
This feature illustrates using zwitch to define a default handler and a specific handler for the 'foo' key. It demonstrates how unhandled keys are processed by the default handler.
{"const zwitch = require('zwitch');\nconst handle = zwitch('key');\n\nhandle.default = (value) => { console.log('Default handler:', value); };\nhandle.handlers.foo = (value) => { console.log('Handled foo:', value); };\n\nhandle({key: 'foo', value: 'bar'});\nhandle({key: 'baz', value: 'qux'});"}
Other packages similar to zwitch
pattern-match
This package provides functionality for pattern matching in JavaScript, similar to functional programming languages. It's comparable to zwitch in enabling conditional logic based on values, but it uses a different syntax and approach, focusing on matching patterns rather than dispatching based on property values.
zwitch
Handle values based on a field.
Contents
What is this?
This is a tiny package that lets you switch
between some field on objects.
When should I use this?
This package is very useful when mapping one AST to another.
It’s a lot like a switch
statement on one field, but it’s extensible.
Install
This package is ESM only.
In Node.js (version 14.14+, 16.0+), install with npm:
npm install zwitch
In Deno with esm.sh
:
import {zwitch} from 'https://esm.sh/zwitch@2'
In browsers with esm.sh
:
<script type="module">
import {zwitch} from 'https://esm.sh/zwitch@2?bundle'
</script>
Use
import {zwitch} from 'zwitch'
const handle = zwitch('type', {invalid, unknown, handlers: {alpha: handleAlpha}})
handle({type: 'alpha'})
function handleAlpha() { }
Or, with a switch
statement:
const field = 'type'
function handle(value) {
let fn = invalid
if (value && typeof value === 'object' && field in value) {
switch (value[field]) {
case 'alpha':
fn = handleAlpha
break
default:
fn = unknown
break
}
}
return fn.apply(this, arguments)
}
handle({type: 'alpha'})
function handleAlpha() { }
function unknown() { }
function invalid() { }
API
This package exports the identifier zwitch
.
There is no default export.
zwitch(key[, options])
Create a switch, based on a key
(string
).
options
Options can be omitted and added later to one
.
options.handlers
Handlers to use, stored on one.handlers
(Record<string, Function>
,
optional).
options.unknown
Handler to use for unknown values, stored on one.unknown
(Function
,
optional).
options.invalid
Handler to use for invalid values, stored on one.invalid
(Function
,
optional).
Returns
See one
(Function
).
one(value[, rest…])
Handle one value.
Based on the bound key
, a respective handler will be called.
If value
is not an object, or doesn’t have a key
property, the special
“invalid” handler will be called.
If value
has an unknown key
, the special “unknown” handler will be called.
All arguments, and the context object (this
), are passed through to the
handler, and it’s result is returned.
one.handlers
Map of handlers (Record<string, Function>
).
one.invalid
Special handler
called if a value doesn’t have a key
property.
If not set, undefined
is returned for invalid values.
one.unknown
Special handler
called if a value does not have a matching
handler.
If not set, undefined
is returned for unknown values.
function handler(value[, rest…])
Handle one value.
Types
This package is fully typed with TypeScript.
It exports the types Handler
, UnknownHandler
, InvalidHandler
, and
Options
.
Compatibility
This package is at least compatible with all maintained versions of Node.js.
As of now, that is Node.js 14.14+ and 16.0+.
It also works in Deno and modern browsers.
Related
Contribute
Yes please!
See How to Contribute to Open Source.
Security
This package is safe.
License
MIT © Titus Wormer