moy-fp/src/Relation/intersectionBy.js

A functional programming library.

import curry from '../Function/curry'

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

export default intersectionBy