functional-utils.js

const noop = arg => arg;

const combine = () => Array.from(arguments).reduce((a, b) => a.concat(b));

const compact = arr => arr.filter(el => el);

const difference = () => {
  var others = Array.from(arguments).slice(1).reduce((a, b) => a.concat(b));
  return arguments[0].filter(el => !others.some(exclude => el === exclude));
};

const head = arr => arr[0];

const initial = arr => arr.slice(0, arr.length-1);

const intersection = () => {
  var len = arguments.length
  return [...Set(
    Array.from(arguments)
      .map(arr => [...Set(arr)])
      .reduce((a, b) => a.concat(b))
      .filter((toFind, i, arr) => arr.filter(el => el === toFind).length == len)
  )]; 
};

const last = arr => arr[arr.length-1];

const max = arr => Math.max(...arr);

const min = arr => Math.min(...arr);

const product = arr => arr.reduce((a, b) => a * b); 

const sortedIndex = (arr, value) => [value].concat(arr).sort().indexOf(value);

const sum = arr => arr.reduce((a, b) => a + b); 

const tail = arr => arr.slice(1);

const union = () => [...Set(
  Array.from(arguments).reduce((a, b) => a.concat(b))
)];

const unique = arr => [...Set(arr)];

const without = () => {
  var values = Array.from(arguments).slice(1);
  return arguments[0].filter(el => !values.some(exclude => el === exclude));
};