0101

function map(arr, iterate){
   var arr2 = []
    arr.forEach(function(value, index, arr){
      arr2.push(iterate(value,index,arr))
    })
    return arr2
}

0102

function find(arr, predicate){
  for(var index = 0; index<arr.length; index++){
    if(predicate(arr[index], index, arr)) return arr[index]
  }
}

0103

function filter(list, predicate) {
  var results = [];
  for (var index = 0; index < list.length; index++) {
    if (predicate(list[index], index, list)) results.push(list[index]);
  }
  return results;
}

0104

function reduce(arr, iteratee, initValue){
  var tmpArr = (initValue === undefined ? [] : [initValue]).concat(arr)
  while(tmpArr.length > 1){
    tmpArr.splice(0, 2, iteratee(tmpArr[0], tmpArr[1]))
  }
  return tmpArr[0]
}

0105

function flatten(arr){
  return arr.reduce(function(initArr, currentArr){
    return initArr.concat(Array.isArray(currentArr)?flatten(currentArr):currentArr)
  }, [])
}
//或者
function flatten2(arr){
  var newArr = []
  function _flat(arr){
    arr.forEach(val=>{
      if(Array.isArray(val)){
        _flat(val)
      }else{
        newArr.push(val)
      }
    })    
  }
  _flat(arr)
  return newArr
}

0201

function byFeild(field){
  return function(user1, user2){
    return user1[field] > user2[field]
  }
}

0202

Array.prototype.equal = function(arr){
  return JSON.stringify(this) === JSON.stringify(arr)
}

0203

Array.prototype.repeat = function(n){
  var result = []
  for(var i=0; i<n; i++){
    result = result.concat(this)
  }
  return result
}

0204

function deepCopy(arr){
  return JSON.parse(JSON.stringify(arr))
}

0205

function copyArray(arr){
  
  var cacheOrigin = []
  var cacheTarget = []
  function copy(arr){
    var newArr = []
    cacheOrigin.push(arr)
    cacheTarget.push(newArr)
    for(var i=0; i<arr.length; i++){
      if(Array.isArray(arr[i])){
        if(cacheOrigin.indexOf(arr[i]) > -1){
          newArr.push(cacheTarget[cacheOrigin.indexOf(arr[i])])
        }else{
          newArr.push(copy(arr[i]))
        }
      }else{
        newArr.push(arr[i])
      }
    }
    return newArr
  }
  return copy(arr)
}