moy-fp/src/Relation/differenceBy.js

A functional programming library.

import curry from '../Function/curry'

/**
 * (a -> String) -> [a] -> [a] -> [a]
 */
const differenceBy = curry(
  (fn, list2, list1) => {
    const differenceObj = {},
          result = []
    for(let item of list2){
      differenceObj[fn(item)] = true
    }
    for(let item of list1){
      if(!differenceObj[fn(item)]){
        result.push(item)
      }
    }
    return result
  }
)

export default differenceBy