functional-javascript-workshop/exercises/basic_reduce/solution/solution.js

The basics of functional programming in JavaScript. No libraries required.

function countWords(arr) {
  return arr.reduce(function(countMap, word) {
    countMap[word] = ++countMap[word] || 1 // increment or initialize to 1
    return countMap
  }, {}) // second argument to reduce initialises countMap to {}
}

module.exports = countWords