Zwitch NPM | npm.io

zwitch

Handle values based on a field.

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.