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https://github.com/planttheidea/switchem

An extensible, functional switch with a chainable API
https://github.com/planttheidea/switchem

functional-programming javascript

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An extensible, functional switch with a chainable API

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README 

        
# switchem










An extensible, functional switch with a chainable API



## Table of contents



* [Usage](#usage)

* [switchem API](#switchem-api)

  * [default](#default)

  * [is](#is)

  * [match](#match)

  * [merge](#merge)

  * [not](#not)

* [Options](#options)

  * [runMatchCallback](#runmatchcallback)

* [Additional methods](#additional-methods)

  * [addCustomCase](#addcustomcase)

* [Browser support](#browser-support)

* [Development](#development)



## Usage



```javascript

import switchem, { addCustomCase } from "switchem";



// create switch statements with the chainable API

const sw1 = switchem()

  .is("foo", "I am foo")

  .not("bar", "I am not bar")

  .default("I must be bar!");



console.log(sw1.match("baz")); // I am not bar

console.log(sw1.match("bar")); // I must be bar!



// extend existing switch statements by simply adding to them

const sw2 = sw1.is(value => {

  return value === "bar";

}, "I am actually bar");



console.log(sw2.match("baz")); // I am not bar

console.log(sw2.match("bar")); // I am actually bar



// or add commonly-used cases for reuse

addCustomCase("isDivisibleBy", (testValue, matchValue) => {

  return matchValue % testValue === 0;

});



console.log(

  switchem()

    .isDivisibleBy(7, "divisible by seven")

    .match(49)

); // divisible by seven

```



## switchem API



#### default



_default(defaultValue: any): Switchem_



Set the default value for the switch, which is returned if none of the cases match.



```javascript

const sw = switchem().default("default");

```



#### is



_is(testValue: any, matchResult: ?any = true): Switchem_



Add a case statement that tests for equality with the `matchValue`.



```javascript

const sw = switchem()

  // functions are executed passing the switched value

  .is(value => {

    return value % 2 === 0;

  }, "I am an even number")

  // regex values are tested via re.test()

  .is(/bar/g, "I contain bar")

  // NaN value comparisons are supported

  .is(NaN, "I am a NaN")

  // static values test for strict equality

  .is("foo", "I am foo");



console.log(sw.match(4)); // I am an even number

console.log(sw.match("bar")); // I contain bar

console.log(sw.match("foo")); // I am foo

```



If you provide a function as a `matchResult`, by default this will be called with both the `testValue` and the

`matchValue`



```javascript

const sw = switchem().is('foo', (testValue, matchValue) => {

  return `${matchValue} match found: ${testValue}`.

});



console.log(sw.match('foo')); // foo match found: foo

```



This setting can be disabled by setting `runMatchCallback` to `false` in `options`.



#### match



_match(matchValue: any): any_



Find the match for `matchValue` based on the existing cases provided in the switch.



```javascript

const sw = switchem().is("foo", "I am foo");



console.log(sw.match("foo")); // I am foo

```



#### merge



_merge(...switchems: Array): Switchem_



Merge the `switchem` instances passed into a new, combined instance.



```javascript

const original = switchem();

const first = switchem()

  .default("defaultValue")

  .is("first", "I am first");

const second = switchem({ runMatchCallback: false }).is(

  "second",

  "I am second"

);



const merged = original.merge(first, second);



// merged is the same as

// switchem({runMatchCallback: false})

//   .default('defaultValue');

//   .is('first', 'I am first')

//   .is('second', 'I am second')

```



#### not



_not(testValue: any, matchResult: ?any = true): Switchem_



Add a case statement that tests for non-equality with the `matchValue`.



```javascript

const sw = switchem()

  // functions are executed passing the switched value

  .not(value => {

    return value % 2 === 0;

  }, "I am an odd number")

  // regex values are tested via re.test()

  .not(/bar/g, "I do not contain bar")

  // static values test for strict equality

  .not("foo", "I am not foo");



console.log(sw.match(3)); // I am an odd number

console.log(sw.match("bar")); // I am not foo

console.log(sw.match("foo")); // I do not contain bar

```



If you provide a function as a `matchResult`, by default this will be called with both the `testValue` and the

`matchValue`



```javascript

const sw = switchem().not('foo', (testValue, matchValue) => {

  return `${matchValue} non-match found: ${testValue}`.

});



console.log(sw.match('bar')); // bar non-match found: foo

```



This setting can be disabled by setting `runMatchCallback` to `false` in `options`.



## Options



#### runMatchCallback



_boolean, defaults to true_



When this option is `true`, then any functions that are used as `matchResult` values will be executed upon match.



```javascript

const sw = switchem().is("foo", (testValue, matchValue) => {

  return [matchValue, testValue];

});



console.log(sw.match("foo")); // ['foo', 'foo']

```



When set to `false`, the method is returned like standard values.



```javascript

const sw = switchem({ runMatchCallback: false }).is(

  "foo",

  (testValue, matchValue) => {

    return [matchValue, testValue];

  }

);



console.log(sw.match("foo")); // (testValue, matchValue) => { return [matchValue, testValue]; }

```



## Additional methods



#### addCustomCase



_addCustomCase(name: string, method: function, isNot: ?boolean): void_



Adds a custom case method to the `switchem` prototype, which provides convenient reuse of a commonly-applied case.



```javascript

// use existing utility methods

import { contains } from "ramda";

import { addCustomCase } from "switchem";



addCustomCase("contains", contains);



const sw1 = switchem().contains("bar", "I contain bar!");



console.log(sw1.match(["foo", "bar", "baz"])); // I contain bar!



// or add your own

addCustomCase(

  "notDivisibleBy",

  (testValue, matchValue) => {

    return matchValue % testValue === 0;

  },

  true

);



const sw2 = switchem().notDivisibleBy(7, "not divisible by seven");



console.log(s2.match(12)); // not divisible by seven

```



This method will be available for all uses of `switchem` after execution, so it is recommended to run this method as

early in your app initialization as possible.



## Browser support



* Chrome (all versions)

* Firefox (all versions)

* Edge (all versions)

* Opera 15+

* IE 9+

* Safari 6+

* iOS 8+

* Android 4+



## Development



Standard stuff, clone the repo and `npm install` dependencies. The npm scripts available:



* `build` => run rolup to build `dist` files

* `dev` => run webpack dev server to run example app / playground

* `dist` => runs `build` and `build-minified`

* `lint` => run ESLint against all files in the `src` folder

* `prepublish` => runs `compile-for-publish`

* `prepublish:compile` => run `lint`, `test:coverage`, `transpile:es`, `transpile:lib`, `dist`

* `test` => run AVA test functions with `NODE_ENV=test`

* `test:coverage` => run `test` but with `nyc` for coverage checker

* `test:watch` => run `test`, but with persistent watcher

* `transpile:lib` => run babel against all files in `src` to create files in `lib`

* `transpile:es` => run babel against all files in `src` to create files in `es`, preserving ES2015 modules (for

  [`pkg.module`](https://github.com/rollup/rollup/wiki/pkg.module))