A functional implementation of switch

functionnal-switch.js

// simple example
const isFruitOrVegetable = switch(
  case('apple', 'isFruit'),
  case('orange', 'isFruit'),
  case('eggplant', 'isVegetable'),
  default('isFruit')
);

isFruitOrVegetable('apple') // isFruit


// We can also pass regular expressions or functions to case.
// For example:
case(
  /apple/, 
  () => 'isFruit'
)

case(
  str => str.includes('eggplant'),
  () => 'isVegetable'
)

We can not use switch, case and default, because they are already used in JavaScript. Need to find other names.

Just come up with some candidates of names:

• switch can be condition;
• case can be when or unless;
• default can be otherwise.

Result:

const isFruitOrVegetable = condition(
  when('apple', 'isFruit'),
  when('orange', 'isFruit'),
  when('eggplant', 'isVegetable'),
  otherwise('isFruit')
);

Perf: http://blog.wax-o.com/2015/05/an-alternative-to-if-else-and-switch-in-javascript/

fall through: https://toddmotto.com/deprecating-the-switch-statement-for-object-literals/

We can achieve 'fall through' cleaner by extracting out common code.

const fruit = str => when(str, 'isFruit')
const vegetable =  str => when(str, 'isVegetable')

const isFruitOrVegetable = condition(
  fruit('apple'),
  fruit('orange'),
  vegetable('eggplant'),
  otherwise('isFruit')
);

To compare with the original switch statement

switch(str) {
case 'eggplant':
  return 'isVegetable';
case 'apple':
case 'orange':
default:
  return 'isFruit';
}

nice (thumb

I have opened a repo for this.