how coding styles change …

before.js

function contains(value){
  var self = this
    , index = 0, l = self.length
  for(;index < l; index++) if(value === self[index]) return true
  return false
}

// …

Array.prototype.contains = contains

now.js

function arrayContains(array, value){
  if(!Array.isArray(array)) {
    throw new TypeError()
  }
  var index = -1
  var length = array.length
  while(++index < length){
    if(value === array[index]) {
      return true
    }
  }
  return false
}

module.exports = arrayContains