moy-fp/src/Relation/union.js

A functional programming library.

import curry from '../Function/curry'
import toString from '../String/toString'

/**
 * [a] -> [a] -> [a]
 */
const union = curry(
  (list2, list1) => {
    const unionObj = {},
          delimiter = String.fromCharCode(0),
          result = []
    let id
    for(let item of list1){
      id = Object.prototype.toString.call(item) + delimiter + toString(item)
      if(!unionObj[id]){
        result.push(item)
        unionObj[id] = true
      }
    }
    for(let item of list2){
      id = Object.prototype.toString.call(item) + delimiter + toString(item)
      if(!unionObj[id]){
        result.push(item)
        unionObj[id] = true
      }
    }
    return result
  }
)

export default union