Programming Language►JavaScript

[JavaScript] forEach, map, reduce 實作

前言

紀錄一下內建函式的實作。

forEach

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Array.prototype.forEach = function(fn){
  for ( var i = 0; i < this.length; i ++ ){
    fn(this[i], i);
  }
}

map

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Array.prototype.map = function(fn){
  var newArray = [];
  for ( var i = 0; i < this.length ; i++ ){
    newArray.push(fn(this[i], i));
  }
  return newArray;
}

reduce

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Array.prototype.reduce = function(fn, initValue){
  var result = initValue || this[0] ;
  var initIndex = initValue ? 0 : 1;
  for ( var i = initIndex; i < this.length; i ++ ){
    result = fn(result, this[i], i);
  }
  return result;
}