zwitch

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.

README

zwitch

Handle values based on a field.

Contents

• What is this?
• When should I use this?
• Install
• Use
• API
  • zwitch(key[, options])
  • one(value[, rest…])
  • function handler(value[, rest…])
• Types
• Compatibility
• Related
• Contribute
• Security
• License

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

• mapz — functional map

Contribute

Yes please! See How to Contribute to Open Source.

Security

This package is safe.

License

MIT © Titus Wormer