johnDash.js

//Re-writing Underscore and LoDash functions.

var forEach = function(collection, callback) {
  for (var key in collection) {
    callback(collection[key]);
  }
};

var map = function(collection, callback) {
  var result = [];
  forEach(collection, function(value) {
    result.push(callback(value));
  });

  return result;
}

var reduce = function(collection, callback, initialValue) {
  var result;
  var isUndefined = typeof initialValue == typeof undefined;
  var isNull = typeof initialValue == typeof null;
  var hasInitialValue = false;
  if (isUndefined == false && isNull == false) {
    hasInitialValue = true;
    result = initialValue;
  } else {
    result = collection[0];
  }
  var index = 0;
  forEach(collection, function(value) {
    if (index === 0 && !hasInitialValue) {
      index++;
      return;
    }
    result = callback(result, value);
  });
  return result;
};

var filter = function(collection, callback){
  var result = [];
  forEach(collection, function(value){
    if(callback(value)===true){
      result.push(value);
    }
  });
  return result;
};

/** Runs a function only once.
 * var test = function(){
 *  console.log("beep")
 *  return 22;
 *}
 * var woo = once(test);
 * woo();
 * this will return "beep" and 22.
 * woo();
 * this will return 22.
 */
var once = function (callback) {
  cachedResult = [];
  return function() {
  if (typeof cachedResult[0] === 'undefined') {
    cachedResult.push(callback());
    return cachedResult;
  }
  
  return cachedResult;
  }
  
}
// New Reduce Implementation
var reduce = function(collection, callback, initialValue) {
  var acc;
  if (!initialValue && !collection) {
  	return 'There is no initialValue or collection';
  }
  if (!callback) {
  	return 'There is no callback';
  }
  if (initialValue) {
  	acc = initialValue
  } else {
  	acc = collection[0] 
    collection = collection.slice(1)
  }
  if (collection) {
    forEach(collection, function(element){
      acc = callback(acc, element)
    })
  }
  return acc
}

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